Question

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:

• A. 17
• B. 20
• C. 40
• D. 50
• E. None of these

Answer 1

The correct option is B

20

Let the numbers be a, b and c. Then, a${}^2$ + b${}^2$ + c${}^2$ = 138 and (ab+bc+ca)=131

( a+b+c)${}^2$=a${}^2$+b${}^2$+c${}^2$+2(ab + bc + ca) = 138+2$\times$131=400

(a + b + c)= $\sqrt{400}$=20