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1. The sum of the squares of three numbers is 138, while the sum of their products taken two at a time is 131. Their sum is –

Answer: Option A

Explanation:

a^{2} + b^{2} + c^{2} = 138 a b + a c + b c = 131 a + b + c = ? Now, we know, {(a + b + c)}^{2} = a^{2} + b^{2} + c^{2} + 2 ab + 2 ac + 2 bc = > {(a + b + c)}^{2} = 138 + 2 \times 131 = > {(a + b + c)}^{2} = 400 = > a + b + c = \sqrt{400} = > a + b + c = 20

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