The average weight of a class of 12 students is 57 kgs. Two students of weights 48 kgs and 68 kgs are replaced by 2 new students having weights 52 kgs and 55 kgs. What is the new average weight of the class?

The average weight of a class of 12 students is 57 kgs. Two students of weights 48 kgs and 68 kgs are replaced by 2 new students having weights 52 kgs and 55 kgs. What is the new average weight of the class? Correct Answer 56.25 kgs

Formula Used:

Average = Sum of weights/Number of students

Calculations:

Average weight of class = 57 kgs

Number of students = 12

Weights of 2 old students = 48 kgs, 68 kgs

Weights of new students = 52 kgs, 55 kgs

Sum of weights of class = 57 × 12 

⇒ Sum of weights of class = 684 kgs

2 old students are replaced be 2 new students

⇒ Sum of weights of class = 684 + (52 + 55) - (48 + 68)

⇒ Sum of weights of class = 675 kgs

New average weight = 675/12 = 56.25 kgs

∴ The new average weight of the class is 56.25 kgs.

Shortcut Trick

Weights of 2 old students = 48 kgs, 68 kgs

Weights of new students = 52 kgs, 55 kgs

Total change in weight = (52 + 55) - (48 + 68) = -9 kgs

⇒ New average weight = 57 - 9/12 = 56.25 kgs

∴ The new average weight of the class is 56.25 kgs.

Bissoy MCQ

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