If a group of four numbers, whose average is 60, the first is one-fifth the sum of the last three. What is the value of the first number?
Explanation:
Sum of the 4 numbers = 60 × 4 = 240
Let the sum of last three numbers be S. ∴ first number = S/5
⇒ S/5 + S = 240 ⇒ 6S/5 = 240 ⇒ S = 200
∴ 1st number = 200/5 = 40
Hence, option (c).
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