Advanced Mathematics Primary 6 Average

The average of 6 numbers is 14. When a 7th number is added, the new average becomes 15. What is the 7th number?

A 1
B 15
C 21
D 99
Show Worked Solution

Worked Solution

Step 1: Find the total of the original 6 numbers. Total = 14 × 6 = 84. Step 2: Find the new total after adding the 7th number. New total = 15 × 7 = 105. Step 3: Find the 7th number. 7th number = 105 − 84 = 21. Answer: The 7th number is 21.

Correct answer: 21

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