MathClubforKids

Olympiad Course for Middle School

Basic Fundamentals

  1. Knowing about numbers

    Example 1: Write the largest 5-digit number.
    Solution: The largest 5-digit number is 99999.

    Example 2: What is the place value of 7 in 4782?
    Solution: The place value of 7 is 700.

    Example 3: Identify whether 4582 is an odd or even number.
    Solution: 4582 is an even number because it ends in 2.

  2. Basic combinatorics

Number system

  1. Test of divisibility

    Example 1: Is 456 divisible by 3?
    Solution: Yes, because the sum of digits (4+5+6=15) is divisible by 3.

    Example 2: Is 1230 divisible by 5?
    Solution: Yes, because it ends in 0.

    Example 3: Is 2145 divisible by 9?
    Solution: No, because the sum of the digits (2+1+4+5=12) is not divisible by 9.

  2. Factors and multiples

    Example 1: What are the factors of 36?
    Solution: The factors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, and 36.

    Example 2: List the first five multiples of 7.
    Solution: 7, 14, 21, 28, 35.

    Example 3: What is the greatest common factor (GCF) of 24 and 36?
    Solution: The GCF of 24 and 36 is 12.

  3. Finding largest/smallest number using digits

    Example 1: Using the digits 3, 9, 1, and 8, form the largest number.
    Solution: 9831.

    Example 2: Using the digits 5, 0, 2, and 7, form the smallest number.
    Solution: 2057.

    Example 3: Using the digits 6, 4, 2, and 9, form the largest odd number.
    Solution: 9643.

  4. Simplification of numbers and Decimals

    Example 1: Simplify 4.56 + 3.789.
    Solution: 4.56 + 3.789 = 8.349.

    Example 2: Simplify 12.45 - 8.62.
    Solution: 12.45 - 8.62 = 3.83.

    Example 3: Simplify 68+48\frac{6}{8} + \frac{4}{8}86​+84​.
    Solution: 68+48=108=1.25\frac{6}{8} + \frac{4}{8} = \frac{10}{8} = 1.2586​+84​=810​=1.25.

  5. Integers and Fractions

    Example 1: What is 5−(−3)5 - (-3)5−(−3)?
    Solution: 5−(−3)=85 - (-3) = 85−(−3)=8.

    Example 2: Multiply 35×27\frac{3}{5} \times \frac{2}{7}53​×72​.
    Solution: 35×27=635\frac{3}{5} \times \frac{2}{7} = \frac{6}{35}53​×72​=356​.

    Example 3: Subtract 34\frac{3}{4}43​ from 111.
    Solution: 1−34=141 - \frac{3}{4} = \frac{1}{4}1−43​=41​.

  6. Playing with numbers

    Example 1: What is the sum of the first 5 prime numbers?
    Solution: 2 + 3 + 5 + 7 + 11 = 28.

    Example 2: Find the product of all even numbers from 1 to 10.
    Solution: 2 × 4 × 6 × 8 × 10 = 3840.

    Example 3: Find the LCM of 8 and 12.
    Solution: LCM of 8 and 12 is 24.

  7. Percentage

    Example 1: What is 20% of 200?
    Solution: 20100×200=40\frac{20}{100} \times 200 = 4010020​×200=40.

    Example 2: If 15% of a number is 75, what is the number?
    Solution: 15100×x=75\frac{15}{100} \times x = 7510015​×x=75. Solving, x=500x = 500x=500.

    Example 3: Increase 250 by 10%.
    Solution: 10% of 250 = 25, so 250 + 25 = 275.

  8. Profit and loss

    Example 1: A pen was bought for $15 and sold for $20. What is the profit percentage?
    Solution: Profit = $5. Profit percentage = 515×100=33.33%\frac{5}{15} \times 100 = 33.33\%155​×100=33.33%.

    Example 2: A toy was bought for $60 and sold for $45. What is the loss percentage?
    Solution: Loss = $15. Loss percentage = 1560×100=25%\frac{15}{60} \times 100 = 25\%6015​×100=25%.

    Example 3: A book costs $100, and a discount of 15% is given. What is the sale price?
    Solution: Discount = 15100×100=15\frac{15}{100} \times 100 = 1510015​×100=15, so the sale price is $85.

Arithmetic Operations

  1. Addition and Subtraction

    Example 1: Add 3456 and 7890.
    Solution: 3456+7890=113463456 + 7890 = 113463456+7890=11346.

    Example 2: Subtract 4231 from 8000.
    Solution: 8000−4231=37698000 - 4231 = 37698000−4231=3769.

    Example 3: What is 12345+6789−234512345 + 6789 - 234512345+6789−2345?
    Solution: 12345+6789−2345=1678912345 + 6789 - 2345 = 1678912345+6789−2345=16789.

  2. Multiplication and division

    Example 1: Multiply 25 by 36.
    Solution: 25×36=90025 \times 36 = 90025×36=900.

    Example 2: Divide 144 by 12.
    Solution: 144÷12=12144 \div 12 = 12144÷12=12.

    Example 3: Divide 1500 by 25.
    Solution: 1500÷25=601500 \div 25 = 601500÷25=60.

  3. LCM & HCF

    Example 1: Find the LCM of 12 and 18.
    Solution: LCM = 36.

    Example 2: Find the HCF of 28 and 42.
    Solution: HCF = 14.

    Example 3: Find the LCM of 8, 12, and 16.
    Solution: LCM = 48.

  4. Magic Squares ,Money

    Example 1: Complete the magic square where each row, column, and diagonal sums to 15:
    [8, 1, 6]
    [_, 5, 7]
    [4, 9, 2]
    Solution: The missing number is 3.

    Example 2: A person has $5, and they spend $3.25. How much do they have left?
    Solution: They have $1.75 left.

    Example 3: If a magic square has a row sum of 18, what is the sum of each diagonal?
    Solution: The sum of each diagonal will also be 18.

  5. Speed,Time

    Example 1: If a car travels 60 km in 2 hours, what is its speed?
    Solution: Speed = 602=30\frac{60}{2} = 30260​=30 km/h.

    Example 2: If a cyclist covers 90 km in 3 hours, what is their speed?
    Solution: Speed = 903=30\frac{90}{3} = 30390​=30 km/h.

    Example 3: How long will it take to travel 150 km at a speed of 50 km/h?
    Solution: Time = 15050=3\frac{150}{50} = 350150​=3 hours.

  6. Word problems on age

    Example 1: John is 5 years older than Mary. In 10 years, John will be twice Mary’s age. How old are they now?
    Solution: Let Mary’s age be xxx. Then John’s age is x+5x + 5x+5. In 10 years, John’s age will be x+15x + 15x+15 and Mary’s will be x+10x + 10x+10. Equation: x+15=2(x+10)x + 15 = 2(x + 10)x+15=2(x+10). Solving, x=5x = 5x=5, so Mary is 5 years old, and John is 10.

    Example 2: Sarah is 3 years older than Tom. Five years ago, Sarah was twice as old as Tom. How old are they now?
    Solution: Sarah is 8 years old, and Tom is 5.

    Example 3: Mary is 10 years younger than her brother. In 4 years, her brother will be 20. How old is Mary now?
    Solution: Her brother is currently 16, so Mary is 6 years old.

  7. Ratio and proportion

    Example 1: The ratio of boys to girls in a class is 3:2. If there are 30 boys, how many girls are there?
    Solution: There are 20 girls.

    Example 2: The ratio of the length to the width of a rectangle is 5:3. If the width is 9 cm, what is the length?
    Solution: The length is 15 cm.

    Example 3: A recipe requires 3 cups of flour for every 2 cups of sugar. If you use 6 cups of flour, how many cups of sugar do you need?
    Solution: You need 4 cups of sugar.

Basic geometry

  1. Rays,angles,Straight lines, parallel lines, Angle properties of triangles

    Example 1: What is the sum of the interior angles of a triangle?
    Solution: The sum of the interior angles of any triangle is always 180∘180^\circ180∘.

    Example 2: If two parallel lines are cut by a transversal, what is the relationship between the corresponding angles?
    Solution: Corresponding angles are equal.

    Example 3: In a right-angled triangle, if one angle is 90∘90^\circ90∘ and another angle is 45∘45^\circ45∘, what is the third angle?
    Solution: The third angle is 180∘−(90∘+45∘)=45∘180^\circ - (90^\circ + 45^\circ) = 45^\circ180∘−(90∘+45∘)=45∘.

  2. Quadrilaterals and Polygons

    Example 1: What is the sum of the interior angles of a quadrilateral?
    Solution: The sum of the interior angles of a quadrilateral is 360∘360^\circ360∘.

    Example 2: How many sides does a polygon have if the sum of its interior angles is 720∘720^\circ720∘?
    Solution: Using the formula (n−2)×180∘=720∘(n-2) \times 180^\circ = 720^\circ(n−2)×180∘=720∘, solve for nnn. The polygon has 6 sides (a hexagon).

    Example 3: What is the sum of the interior angles of a pentagon?
    Solution: (5−2)×180∘=540∘(5-2) \times 180^\circ = 540^\circ(5−2)×180∘=540∘.

  3. Problems on square,rectangle and circles

    Example 1: Find the area of a square with a side length of 6 cm.
    Solution: Area = side2=6×6=36\text{side}^2 = 6 \times 6 = 36side2=6×6=36 square cm.

    Example 2: What is the perimeter of a rectangle with a length of 10 cm and a width of 4 cm?
    Solution: Perimeter = 2×(10+4)=282 \times (10 + 4) = 282×(10+4)=28 cm.

    Example 3: If the radius of a circle is 7 cm, what is the circumference?
    Solution: Circumference = 2×π×7=442 \times \pi \times 7 = 442×π×7=44 cm (using π≈3.14\pi \approx 3.14π≈3.14).

Solid Geometry

  1. 3D shapes and critical thinking problems

    Example 1: How many faces does a cube have?
    Solution: A cube has 6 faces.

    Example 2: How many vertices does a rectangular prism (cuboid) have?
    Solution: A rectangular prism has 8 vertices.

    Example 3: How many edges does a cylinder have?
    Solution: A cylinder has 2 edges.

Statistics

  1. Verage,Piechart

    Example 1: The test scores of 5 students are 80, 85, 90, 95, and 100. Find the average score.
    Solution: Average = 80+85+90+95+1005=90\frac{80+85+90+95+100}{5} = 90580+85+90+95+100​=90.

    Example 2: In a pie chart, 50% of the chart represents students who like apples, 30% represents those who like bananas, and 20% represents those who like oranges. What fraction of students like oranges?
    Solution: 20100=15\frac{20}{100} = \frac{1}{5}10020​=51​.

    Example 3: If the average of three numbers is 50, and two of the numbers are 60 and 40, find the third number.
    Solution: Let the third number be xxx. Then, 60+40+x3=50\frac{60+40+x}{3} = 50360+40+x​=50. Solving, x=50x = 50x=50.

  2. Graphs,data handling

    Example 1: A bar graph shows the number of books read by 4 students: 5, 8, 12, and 9. How many books were read in total?
    Solution: Total = 5+8+12+9=345 + 8 + 12 + 9 = 345+8+12+9=34 books.

    Example 2: In a line graph, if the temperature rises from 20°C to 30°C over 5 hours, what is the average increase in temperature per hour?
    Solution: Average increase = 30−205=2\frac{30 - 20}{5} = 2530−20​=2°C per hour.

    Example 3: How many students liked vanilla if a pictograph shows 6 symbols of ice creams, where each symbol represents 5 students?
    Solution: 6×5=306 \times 5 = 306×5=30 students liked vanilla.

Algebra Basics

  1. Introduction ,Properties of algebra

    Example 1: Solve for xxx: 2x+5=152x + 5 = 152x+5=15.
    Solution: 2x=102x = 102x=10, so x=5x = 5x=5.

    Example 2: Solve for yyy: 3y−8=193y - 8 = 193y−8=19.
    Solution: 3y=273y = 273y=27, so y=9y = 9y=9.

    Example 3: What is the distributive property in algebra?
    Solution: The distributive property is a(b+c)=ab+aca(b + c) = ab + aca(b+c)=ab+ac.

  2. problems on variable and constants

    Example 1: In the equation 2x+3=92x + 3 = 92x+3=9, identify the variable and the constant.
    Solution: The variable is xxx, and the constant is 3.

    Example 2: Solve for xxx: 5x+4=195x + 4 = 195x+4=19.
    Solution: 5x=155x = 155x=15, so x=3x = 3x=3.

    Example 3: In the expression 3y−73y - 73y−7, what is the coefficient of yyy?
    Solution: The coefficient of yyy is 3.

  3. word problems on Algebra

    Example 1: If John’s age is 3 years more than twice his sister’s age, and his sister is 8 years old, how old is John?
    Solution: John’s age = 2×8+3=192 \times 8 + 3 = 192×8+3=19 years.

    Example 2: The length of a rectangle is 5 cm more than its width. If the perimeter is 40 cm, what are the dimensions of the rectangle?
    Solution: Width = 7.5 cm, Length = 12.5 cm.

    Example 3: A number is tripled and then decreased by 7. The result is 11. What is the number?
    Solution: The number is 6.

Mathematcal Reasoning

  1. Finding number of plane figures

    Example 1: How many triangles can be formed in a hexagon by connecting vertices?
    Solution: You can form 6 triangles.

    Example 2: How many diagonals does a pentagon have?
    Solution: A pentagon has 5 diagonals.

  2. Paper cutting and folding

    Example 1: A square paper is folded in half and then in half again. How many sections are there when the paper is unfolded?
    Solution: 4 sections.

    Example 2: A circle is folded twice. How many visible creases will there be when the circle is unfolded?
    Solution: There will be 2 creases.

  3. Math puzzles

    Example 1: A train travels 100 miles in 2 hours. How long will it take to travel 250 miles at the same speed?
    Solution: It will take 5 hours.

    Example 2: If two workers can paint a wall in 4 hours, how long will it take 3 workers to paint the same wall?
    Solution: It will take 4×23=83\frac{4 \times 2}{3} = \frac{8}{3}34×2​=38​ hours (2 hours and 40 minutes).

  4. Mirror images and relationships

    Example 1: What is the mirror image of the letter “E”?
    Solution: The mirror image of “E” is “Ǝ”.

    Example 2: If a triangle’s mirror image is shown, which side will appear opposite?
    Solution: The right side will appear on the left, and vice versa.

  5. Clock and calendar

    Example 1: What time will it be 3 hours after 5:00 PM?
    Solution: It will be 8:00 PM.

    Example 2: If today is Monday, what day will it be 10 days from now?
    Solution: It will be Thursday.

  6. Net cube and Dice

    Example 1: If a cube is unfolded into a net, how many squares will the net have?
    Solution: The net will have 6 squares.

    Example 2: If a die shows 3 on one face, what will be on the opposite face?
    Solution: The opposite face will show 4 (standard die).

  7. Direction and patterns

    Example 1: A person walks 10 meters north, then 15 meters west, and finally 5 meters south. What is their final position relative to the starting point?
    Solution: The person is 10 meters west and 5 meters north of the starting point.

    Example 2: Identify the next shape in the pattern: Circle, Triangle, Square, Circle, Triangle, ___.
    Solution: The next shape is a Square.

Symmetry

  1. Axes of symmety,rotational

    Example 1: How many lines of symmetry does an equilateral triangle have?
    Solution: An equilateral triangle has 3 lines of symmetry.

    Example 2: What is the order of rotational symmetry of a regular pentagon?
    Solution: The order of rotational symmetry is 5.

    Example 3: Does a rectangle have rotational symmetry?
    Solution: Yes, it has rotational symmetry of order 2.

Basic Combinatorics

  1. Sitting arrangement

    Example 1: How many ways can 4 people sit in a row?
    Solution: 4!=244! = 244!=24 ways.

    Example 2: How many ways can 3 people sit in a circle?
    Solution: (3−1)!=2(3-1)! = 2(3−1)!=2 ways.

  2. Arrangement of objects

    Example 1: How many ways can the letters of the word "MATH" be arranged?
    Solution: 4!=244! = 244!=24 ways.

    Example 2: How many ways can you arrange 5 books on a shelf?
    Solution: 5!=1205! = 1205!=120 ways.

Verbal reasoning

  1. Problems practice-1

    Example 1: "All birds have wings. Some animals are birds." Can we conclude that some animals have wings?
    Solution: Yes.

    Example 2: "Some fruits are apples. All apples are fruits." Can we conclude that all fruits are apples?
    Solution: No.

  2. Problems practice-2

    Example 1: If it rains, the ground gets wet. The ground is wet. Did it rain?
    Solution: Not necessarily, something else may have caused the ground to get wet.

    Example 2: If a person is standing in the rain without an umbrella, they get wet. John is standing in the rain without an umbrella. Is John wet?
    Solution: Yes, John is wet.

Mensuration

  1. Perimeter of plane figure

    Example 1: Find the perimeter of a rectangle with length 8 cm and width 5 cm.
    Solution: Perimeter = 2×(8+5)=262 \times (8 + 5) = 262×(8+5)=26 cm.

    Example 2: Find the perimeter of a triangle with sides 3 cm, 4 cm, and 5 cm.
    Solution: Perimeter = 3+4+5=123 + 4 + 5 = 123+4+5=12 cm.

  2. Area of plane figures

    Example 1: Find the area of a rectangle with length 7 cm and width 3 cm.
    Solution: Area = 7×3=217 \times 3 = 217×3=21 square cm.

    Example 2: Find the area of a triangle with base 6 cm and height 4 cm.
    Solution: Area = 12×6×4=12\frac{1}{2} \times 6 \times 4 = 1221​×6×4=12 square cm.

Mathematical Logic

  1. Statement related questions

    Example 1: "If it is raining, the grass is wet. The grass is wet." Can we conclude that it is raining?
    Solution: No, there could be another reason the grass is wet.

    Example 2: "All dogs are animals. Some animals are pets." Can we conclude that some dogs are pets?
    Solution: Yes.

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