Question

The average weight of a group of $6$ students is $41$ kg . A student weighing $38$ kg left the group and a new student joined the group . Now the average weight has changed to $42$ kg . What is the weight of the new student ?

Answer 1

Sum of the weight of the student = $average\times number$ $=41\times 6=246$

Let the weight of the student who leave the class is $38$ so new sum $=246-38=208$

After joining the student of weight $x$ kg

New sum $=208+x$ $........\left(i\right)$

After joining the student of weight $x$ kg avg. become $42$ so

New sum $=42\times 6=252$$.......\left(ii\right)$

Now, from equation (i) and (ii)

$208+x=252$

$x=252-208=44kg$

Hence, the weight of the new student is $44$ kg .