WAEC 2022 Mathematics · Question 29

The mean of two numbers x and y is 4. Find the mean of four numbers x, 2x, y and 2y

Options

Answer: C. 6

Explanation written with AI and checked against the answer key

Analyze the question: We're told the mean of x and y is 4, and we need the mean of the four numbers x, 2x, y and 2y. Concept: Mean = (sum of the numbers) ÷ (how many numbers there are). Solution: Step 1: Use the first piece of information. (x + y) / 2 = 4 So x + y = 8 Step 2: Add up the four numbers. x + 2x + y + 2y = 3x + 3y = 3(x + y) Step 3: Substitute x + y = 8. 3(8) = 24 Step 4: Divide by 4 (there are four numbers). Mean = 24 ÷ 4 = 6 Check with an example: Let x = 3 and y = 5 (their mean is 4). The four numbers are 3, 6, 5, 10. Sum = 24, and 24 ÷ 4 = 6. ✔ The correct option is C. **Tip: When a question gives you a mean, immediately convert it to a sum (mean × count). Here, the four numbers are just 1.5 times the original two numbers' contribution, so the new mean is 4 × 1.5 = 6. Looking for factoring shortcuts like 3(x + y) saves time in the exam.

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