GMAT® Practice Question - Arithmetic Mean

Concept: Computing average. Computing sum from average.

This GMAT quant practice question is a problem solving question from Descriptive Statistics. Concept: Compute the average after a new element is added to an existing set of data. An easy question.

Question: The average weight of a group of 30 friends increases by 1 kg when the weight of their football coach was added. If average weight of the group after including the weight of the football coach is 31 kg, what is the weight of their football coach?

  1. 31 kg
  2. 61 kg
  3. 60 kg
  4. 62 kg
  5. 91 kg

Video Explanation

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Explanatory Answer

The new average weight of the group after including the football coach = 31 kg.
As the new average is 1 kg more than the old average, old average without including the football coach = 30 kg.

Standard Framework
Description Number Average Sum
Without Coach 30 30 900
With Coach 31 31 961
Weight of coach     961 - 900 = 61 kg

The total weight of the 30 friends without including the football coach = 30 * 30 = 900.
After including the football coach, the number people in the group increases to 31 and the average weight of the group increases by 1 kg.

Therefore, the total weight of the group after including the weight of the football coach = 31 * 31 = 961 kg.
Therefore, the weight of the football coach = 961 - 900 = 61 kg.

Choice B is the correct answer.

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