The average weight of 49 students in a class is 39 kg. Seven of them whose average weight is 40 kg leave the class and other seven students whose average weight is 54 kg join the class. What is the new average weight (in kg) of the class?

Question

Question

This question was previously asked in

SSC CGL 2022 Tier-I Official Paper (Held On : 02 Dec 2022 Shift 4)

Answer 1

Given:

The average weight of 49 students in a class is 39 kg.

Concept used:

Average = Sum of elements/Number of elements

Calculation:

Total weight of the 49 students = 39 × 49

⇒ 1911

According to the question,

New total weight = 1911 - 40 × 7 + 54 × 7

⇒ 1911 - 280 + 378

⇒ 2009

New average = 2009/49

⇒ 41 kg

∴ The new average weight (in kg) of the class is 41.

Shortcut Trick

Seven students of average weight 40 kg leave and Seven students of average weight 54 kg join.

So, net weight gain (54 - 40) × 7 = 98 kg

This extra will be distributed among 49 people, so average will increase 98/49 = 2 kg

The new average weight 39 + 2 = 41 kg