The sum of the squares of three number is 138,while the sum of their products taken two at a time is 131. their sum is :  Choose the most appropriate option.
A) 20	B) 30	C) 40	D) None of these	E) Cannot be determined
Solution   Let the numbers be a,b and c then, a 2 + b 2+ c 2 = 138 and (ab + b c + ac) = 131.   (a + b+ c)2 = a 2 + b 2 + c 2 + 2(ab + b c + ca) = 138 + 2 * 131= 
<gadget id="calculator">138 + 2 * 131</gadget>
<output>400</output>
400 .   ⇒ (a + b + c)= 400/20= 
<gadget id="calculator">400/20</gadget>
<output>20</output>
20   20nswer 20
<result>A</result>
The sum of the squares of three number is 138,while the sum of their products taken two at a time is 131. their sum is :