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average problem

by rahul.s » Mon Feb 01, 2010 5:32 am
The average of marks obtained by 120 candidates in a certain examination is 35. If the average of passed candidates is 39 and that of the failed candidates is 15. How many candidates passed the examination?

there are no options for this problem.

could someone help me with the approach?

OA: 100
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by thephoenix » Mon Feb 01, 2010 5:38 am
eqn is
120*35=39*x+(120-x)*15

solving x=100
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by sars72 » Mon Feb 01, 2010 5:40 am
total marks = 120 * 35 = 4200

number who passed= x

number who failed = 120 -x

--> 39x + 15(120-x) = 4200

--> 39x - 15 x + 1800 = 4200

--> 24x = 2400

--> x= no. who passed = 100
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