Question
Out of four numbers, the average of the first three is
16 and that of the last three is 15. If the last number is 21 then the first number is:Solution
The last 3 numbers total = 3 × 15 = 45 So the middle 2 numbers will add to 45 – 21 = 24 First 3 numbers total = 3 × 48 = 48 So the first number is 48 – 24 = 24 ∴ The first number is 24
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