WAEC 2010 Mathematics · Question 21

The mean age of R men in a club is 50 years, Two men aged 55 and 63, left the club and the mean age reduced by 1 year. Find the value of R

Options

A.18
B.20
C.22
D.28

Answer: B. 20

Explanation written with AI and checked against the answer key

Analyze the question: R men have a mean age of 50. Two men (aged 55 and 63) leave, and the new mean of the remaining (R − 2) men is 49. Concept: Mean = Total sum ÷ Number of items, so Sum = Mean × Number. Solution: Original total age = 50R After the two men leave, the total age = 50R − (55 + 63) = 50R − 118 Number of men left = R − 2, and the new mean = 49: 50R − 118 = 49(R − 2) 50R − 118 = 49R − 98 50R − 49R = 118 − 98 R = 20 Check: Original total = 50 × 20 = 1000. After removal: 1000 − 118 = 882. Remaining men = 18. 882 ÷ 18 = 49 ✓ Answer: R = 20, which is option B. Tip: For "mean changes after removing or adding items" questions, always write the total as Mean × Number before and after the change, then set up one equation. Always verify by substituting back.

AI can make mistakes. Report anything that looks wrong.