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:
Select the correct option:
A) 20
B) 30
C) 40
D) 50
E) 60
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+2x131= 400.   (a + b + c) = square root of 400 = 20   answer :20
<result>A</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: