A group of boys has an average weight of 36 ,kg . One boy weighing 42 ,kg leaves group and another b

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A group of boys has an average weight of $36 \,kg$. One boy weighing $42 \,kg$ leaves the group and another boy weighing $30\, kg$ joints the group. If the average now becomes $35.7\, kg$, then how many boys are there in the group?

A

$30$

B

$32$

C

$40$

D

$56$

Solution

Let the $No.$ of boys in the group be $x$

$\frac{x \times 36-42+30}{x}=35.7$

$36 x-12=35.7 x$

$3 x=12$

$x=40$

Standard 13

Quantitative Aptitude

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