GMAT Maths | GMAT Statistics Question 3

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. A GMAT 550 level quant sample question.

Question 3: 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

---

---

Explanatory Answer

The group comprises 30 friends.
When the football coach is also included, the average weight of the group becomes 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 to Solve Averages Questions

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 of 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.