This question was previously asked in

DSSSB TGT Social Studies Female General Section - 14 Nov 2018 Shift 1

Option 4 : 15

Given:

The average weight of some children in a camp was 24 kg.

10 children having average weight 98/4 kg left the camp.

5 children having average weight 18 kg joined the camp.

Formula used:

Average weight = Total weight/Number of people

Calculation:

Let total number of children in the camp be x

Average weight of x children = 24

Sum of weight of x children = 24x

Average weight of 10 children = 98/4

Sum of weight of 10 children = 98/4 × 10 = 245

Average weight of 5 children = 18

Sum of weight of 5 children = 18 × 5 = 90

According to the question,

24(x + 5 - 10) = 24x – 245 + 90

24(x - 5) – 155 = 24x

⇒ x = 15

∴ initially 15 children were in the camp.