AlgebraHardTwo numbers from their sum and difference
Algebra practice question
The sum of two numbers is 15 and their difference is 3. What is the product of the two numbers?
Answer: 54
Let the numbers be a and b with a + b = 15 and a − b = 3. Adding: 2a = 18, a = 9; then b = 6. Product: 9 × 6 = 54.
Common wrong answers
- If you answered 6
- 6 is the smaller number, not the product.
- If you answered 9
- 9 is the larger number, not the product.
- If you answered 45
- 45 is 15 × 3, multiplying the sum by the difference. Find the two numbers first: 9 and 6.
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