Multiple choice general knowledge math & puzzles

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 31kgs, what is the weight of their football coach in kgs?

  1. 31

  2. 61

  3. 60

  4. 62

  5. 91
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the original sum of 30 friends' weights be S. The new average after adding the coach is 31 kg for 31 people, so total weight = 31 × 31 = 961 kg. The average increased by 1 kg, so original average was 30 kg, giving S = 30 × 30 = 900 kg. Coach's weight = 961 - 900 = 61 kg. Option B is correct. Option C (60) ignores that the coach raises the average by 1 kg for 31 people.

AI explanation

With 30 friends, if adding one more person (the coach) raises the average by 1 kg to a new average of 31 kg over 31 people, the original total weight was 30 x 30 = 900 kg and the new total is 31 x 31 = 961 kg. The coach's weight is the difference: 961 - 900 = 61 kg.

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