Problems on Numbers - Quantitative Aptitude (MCQ) questions for Q. 76

Q.  Sum of products of three numbers taken two at a time is 131. Sum of squares of the three numbers is 138. What is the sum of the three numbers?
- Published on 12 Jun 15

a. 25
b. 30
c. 20
d. 22

ANSWER: 20
 
All the data given in the question points to the equation mentioned below:

Considering the three numbers to be a,b and c:
(a+b+c)2 = a2 + b2 + c2 + 2ab + 2bc + 2ca

Accordingly, substitute for a, b and c and solve:

=> a2+b2+c2= 138, ab+bc+ac = 131. Thus, 2(ab+bc+ac)= 2*131= 262

(a+b+c)2= 138+262= 400.

Therefore, a+b+c= 20

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