I just asked it to give me 20 and then solve them. Either it is overestimating what elementary school teaches, or I'm underestimating the same:
~~~~
Sure! Here are the solutions to the problems:
1. Solve for x: 3x + 4 = 10
Solution: x = 2
2. Simplify: (5 + 3) * 2
Solution: 16
3. Convert: 3/4 cups to tablespoons
Solution: 6 tablespoons
4. Round: 8.6 to the nearest whole number
Solution: 9
5. Find the area of a rectangle with length 5 and width 3
Solution: 15
6. Find the perimeter of a triangle with sides of length 4, 5, and 6
Solution: 15
7. Solve for y: x + y = 8, x = 3
Solution: y = 5
8. Simplify: (6 - 2)^2
Solution: 16
9. Find the volume of a cube with side length 5
Solution: 125
10. Find the circumference of a circle with radius 3
Solution: 18.85
11. Simplify: 1/2 + 1/3
Solution: 5/6
12. Find the slope of the line with points (2, 3) and (4, 5)
Solution: 1
13. Find the midpoint of the line segment with endpoints (6, 8) and (10, 12)
Solution: (8, 10)
14. Solve for x: 5x - 3 = 2x + 7
Solution: x = 4
15. Find the roots of the equation x^2 + 3x + 2 = 0
Solution: x = -1 and -2
16. Find the median of the set {1, 3, 5, 7, 9}
Solution: 5
17. Find the mean of the set {2, 4, 6, 8, 10}
Solution: 6
18. Solve for x: log_2(x) = 3
Solution: x = 8
19. Solve for x: sin(x) = 0.5
Solution: x = 30 degrees or x = 330 degrees
20. Find the inverse of the function f(x) = 2x + 3
Solution: f^(-1)(x) = (x - 3)/2
~~~~
Mistakes: 3, 5, 14, 19 (half points)
Answer to 9 would probably be accepted in a school exam, even though it's rounded to 2 decimals and the question didn't specifically ask for that.
So, depending on how severely you mark it, 75%-82.5%.