Seventh Grade - Math Olympiad

Seventh grade Math Olympiad

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1. A recipe calls for 2 1/2 cups of flour for every 1 1/4 cups of sugar. If you want to make a larger batch using 5 cups of flour, how many cups of sugar will you need?

Solution
Correct: A
Let f be the amount of flour and s be the amount of sugar. We have the proportion f/s = 2.5/1.25. We are given f = 5. Thus, 5/s = 2.5/1.25. Cross-multiplying, we get 2.5s = 5 * 1.25 = 6.25. Dividing by 2.5 gives s = 6.25 / 2.5 = 2.5. So the answer is 2 1/2.

2. A store marks up a shirt by 40% and then puts it on sale for 20% off. If the shirt originally cost the store 15, what is the final sale price?

Solution
Correct: A
The shirt is marked up by 40%, so the new price is 15 + 0.40 * 15 = 15 + 6 = 21. Then it's discounted by 20%, so the final price is 21 - 0.20 * 21 = 21 - 4.20 = 16.80.

3. Solve for x: 3(x + 2) - 5 = 2(x - 1) + 4

Solution
Correct: B
Expanding, we get 3x + 6 - 5 = 2x - 2 + 4. This simplifies to 3x + 1 = 2x + 2. Subtracting 2x from both sides gives x + 1 = 2. Subtracting 1 from both sides gives x = 1.

4. What is the area of a circle with a circumference of 10π?

Solution
Correct: C
Circumference C = 2πr. We are given that 10π = 2πr, so r = 5. Area A = πr^2 = π(5^2) = 25π.

5. A train travels 120 miles in 2 hours. At the same rate, how long will it take to travel 300 miles?

Solution
Correct: B
The train's rate is 120 miles / 2 hours = 60 miles per hour. To travel 300 miles at 60 mph will take 300 / 60 = 5 hours.

6. What is the value of (-3)^3 + (-2)^2 - (-1)^5?

Solution
Correct: B
(-3)^3 = -27, (-2)^2 = 4, and (-1)^5 = -1. Therefore, -27 + 4 - (-1) = -27 + 4 + 1 = -22.

7. A triangle has angles measuring x, 2x, and 3x degrees. What is the measure of the largest angle?

Solution
Correct: C
The angles of a triangle sum to 180 degrees. So x + 2x + 3x = 180, which means 6x = 180. Therefore, x = 30. The largest angle is 3x = 3(30) = 90 degrees.

8. If a = -2 and b = 3, what is the value of a^2 - 2ab + b^2?

Solution
Correct: C
Substituting, we get (-2)^2 - 2(-2)(3) + (3)^2 = 4 + 12 + 9 = 25.

9. A square has a perimeter of 36. What is the area of the square?

Solution
Correct: C
If the perimeter of a square is 36, then each side has length 36/4 = 9. The area of the square is 9*9 = 81.

10. What is 20% of 80% of 150?

Solution
Correct: B
80% of 150 is 0.80 * 150 = 120. 20% of 120 is 0.20 * 120 = 24.

11. A bag contains 5 red marbles, 3 blue marbles, and 2 green marbles. What is the probability of selecting a blue marble at random?

Solution
Correct: B
The total number of marbles is 5 + 3 + 2 = 10. The probability of selecting a blue marble is the number of blue marbles divided by the total number of marbles, which is 3/10.

12. If x/3 + 2 = 7, what is the value of x?

Solution
Correct: C
Subtracting 2 from both sides gives x/3 = 5. Multiplying both sides by 3 gives x = 15.

13. Which of the following is equivalent to 3/8?

Solution
Correct: C
3/8 = 0.375.

14. Two complementary angles are in the ratio 2:3. What is the measure of the smaller angle?

Solution
Correct: B
Complementary angles add up to 90 degrees. Let the angles be 2x and 3x. So, 2x + 3x = 90, which means 5x = 90. Therefore, x = 18. The smaller angle is 2x = 2(18) = 36 degrees.

15. Simplify: (4x^2y^3)(2x^3y)

Solution
Correct: B
(4x^2y^3)(2x^3y) = (4*2)(x^2*x^3)(y^3*y) = 8x^(2+3)y^(3+1) = 8x^5y^4.

16. What is the median of the following numbers: 5, 8, 2, 9, 1, 4, 6?

Solution
Correct: B
First, order the numbers: 1, 2, 4, 5, 6, 8, 9. The median is the middle number, which is 5.

17. A rectangular prism has dimensions 3 cm x 4 cm x 5 cm. What is its surface area?

Solution
Correct: C
The surface area is 2(lw + lh + wh) = 2(3*4 + 3*5 + 4*5) = 2(12 + 15 + 20) = 2(47) = 94 cm^2.

18. Solve the inequality: 2x - 3 < 7

Solution
Correct: B
Add 3 to both sides: 2x < 10. Divide both sides by 2: x < 5.

19. Which ratio is proportional to 4:6?

Solution
Correct: C
The simplified ratio 4:6 is 2:3. We need to find another ratio that simplifies to 2:3. 8:12 simplifies to 2:3, since 8/12 = 2/3.

20. If a store sells pencils for 50 cents each, and erasers for 75 cents each, how much will it cost to buy 6 pencils and 4 erasers?

Solution
Correct: C
6 pencils will cost 6 * 0.50 = 3.00. 4 erasers will cost 4 * 0.75 = 3.00. The total cost is 3.00 + 3.00 = 6.00.

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