Answer: 4 science questions and 5 math questions
Explanation:
To guess, you know that no matter how many 10 point questions you answer, the result will end in a zero. The number given is 85 so find a number you can multiply by 9 that ends in a 5. Answer: 9(5) = 45
The remaining points (40) are divisible by 10.
40 ÷ 10 = 4
Check: 5 (9-point questions) + 4 (10-point questions) = 9 total questions
45 points + 40 points = 85 points
Note that this problem can be solved mathematically by setting up a system of equations:
Points: 9x + 10y = 85
Quantity: x + y = 9