Question

The average weight of students in a class was 60.5 kg. When 8 students, whose average weight was 65 kg, joined the class, then the average weight of all the students increased by 0.9 kg. The total number of students now in the class is:
1. 35
2. 40
3. 32
4. 27

Answer 1

Correct Answer - Option 2 : 40

Given:

The average weight of students in class = 60.5 kg

When 8 students  joined in class average weight = 65

The average weight of all students is increased = 0.9

Concept Used:

Sum = Average × Number of observation

Calculations:

Let the number of students initially be 'x'

Total weight of students initially = 60.5 × x

Total weight of total students = 65 × 8

⇒ 520

Total number of students after 8 students joined in class = x + 8

Increased average = 60.5 + 0.9

⇒ 61.4

Total weight of students = 520 + 60.5x

⇒ 61.4(x + 8) = 520 + 60.5x

⇒ 61.4x + 492.2 = 520 + 60.5x

⇒ 0.9x = 520 - 491.2

⇒ x = 28.8/0.9

⇒ x = 32

Total number of students = x + 8

⇒ 32 + 8 = 40

∴ The number of students in class is 40