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:
20
30
40
None of these
Explanation:
Let the three numbers be a, b and c.
According to the given condition
=>$ a^2 + b^2 + c^2 $= 138.
ANd, ab + bc + ca = 131.
Now, we know that $(a+b+c) ^2$ =$a^2 + b^2 + c^2$ + 2(ab+bc+ca)
On taking values we get$ (a+b+c) ^2$ = 138 + 2(131) = 400
=> a + b + c = 20.