Subject: General Aptitude · Chapter: Problems on Numbers · Exam: 1999 · Marks: · Difficulty:
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)20
(b)30
(c)40
(d)None of these
Answer
Answer (as printed): A
Explanation
Let the numbers be $a, b$ and $c$. Then, $a^{2}+b^{2}+c^{2}=138$ and $(ab+bc+ca)=131$. $(a+b+c)^{2}=a^{2}+b^{2}+c^{2}+2(ab+bc+ca)=138+2\times131=400 \Rightarrow (a+b+c)=\sqrt{400}=20$.
Explanation as extracted from the printed page; notation may be imperfect.