The average of marks obtained by 120 boys was 40. If the average of marks of passed boys was 39 and that of failed boys was 15, the number of boys who passed the examination is?
Choose the correct choice from the following choices:
A) 100	B) 110	C) 125	D) 130	E) 145
Let the number of boys who passed = X.   Then, 39 x X + 15 x (120 - X) = 120 x 40   24X = 4800 - 1800   =&gt; X = 3000/24= 
<gadget id="calculator">3000/24</gadget>
<output>125</output>
125   Hence, the number of boys passed= 125.   ANSWER:125
<result>C</result>
The average of marks obtained by 120 boys was 40. If the average of marks of passed boys was 39 and that of failed boys was 15, the number of boys who passed the examination is?