If a + b = 10 and a - b = 4, then a × b equals
A24
B30
C18
D21
Answer & Solution
Correct answer: D. 21
Add: 2a = 14, so a = 7. Subtract: 2b = 6, so b = 3. Product = 7 × 3 = 21. Verify: 7 + 3 = 10 ✓; 7 - 3 = 4 ✓.
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