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 Pick one:
A) 15
B) 20
C) 25
D) 35
E) 45
Explanation:   Let the numbers be a, b and c.   Then,   a2+b2+c2=138   and (ab + bc + ca) = 131   (a+b+c)2=a2+b2+c2+2(ab+bc+ca)   = 138 + 2 x 131 = 400   =&gt;(a+b+c)=400−−−√=20.   Option 20
<result>B</result>
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