Question

The average weight of N boys in a group is 36 kg. If 20 other boys whose average weight is 30 kg join the group, the average weight of the group would be the same as what it would be if 5 boys whose average weight is 40 kg leave the group. Find N.​

Answer 1

Answer:

10

Step-by-step explanation:

(36N + 20*30)/(N+20) = (36N - 5*40)/(N-5),

36N^2 + 600N - 180N - 3000 = 36N^2 -200N + 720N -4000,

420N  - 3000 = 520N - 4000,

N = 10

Answer 2

Answer:

The value if N=10

Step-by-step explanation:

Given that,

Average weight of N boys is 36kg

Therefore total weight of N boys is given as

$N \times 36 =( 36N)kg$

Given that,20 other boys whose average weight is 30kg join the group.Therefore their total weight is

$20 \times 30 = 600kg$

Now total weight is given as

$(36N + 600)kg$

and total no.of boys are

$N + 20$

If 5 boys whose average weight is 40kg leave the group,the total weight leaving group is

$40 \times 5 = 200kg$

The boys left is

$(N - 5) \: boys$

Now according to given question,we can write a relation

$\frac{36N + 600}{N + 20} = \frac{36N - 200}{N - 5}$

on cross multiplying we get

$36N {}^{2} + 420N - 3000 = 36N {}^{2} + 520N - 4000 \\ = = > N = 10$

Therefore,N=10

#SPJ3