The sum of two numbers is 25 and their difference is 9. What is their product?
To solve this problem, I need to find the two numbers that satisfy the given conditions. Let me call them x and y, so that x + y = 25 and x - y = 9. I could try to solve this system of equations by elimination or substitution, but I notice that if I add the two equations together, I get 2x = 34, which means x = 17. Then, using either equation, I can find y by plugging in x = 17. For example, 17 + y = 25, so y = 25 - 17 = 8. Now that I have the two numbers, I can find their product by multiplying them: 17 * 8 = 136. 