Exams › SSC CGL (Prelims) › General

If a^3 + b^3 = 91 and ab = 12, what is the value of a + b?

1. 6
2. 7
3. 8
4. 9

Correct answer: 7

Solution

Using (a+b)^3 = a^3 + b^3 + 3ab(a+b), let s = a+b. Then s^3 = 91 + 36s. Testing s = 7: 343 = 91 + 252 = 343, which holds, so a + b = 7.

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