Question
The average of 5 numbers is 28. The average of the first
3 numbers is 25 and the average of the last 3 numbers is 31. Find the third number.Solution
Let the numbers be a, b, c, d, e. Total sum = 5 × 28 = 140 a + b + c = 3 × 25 = 75 c + d + e = 3 × 31 = 93 Also, a + b + c + d + e = 140 ⇒ (a + b + c) + (d + e) = 140 ⇒ 75 + (d + e) = 140 ⇒ d + e = 65 Now, c + d + e = 93 ⇒ c + 65 = 93 ⇒ c = 28 Answer: 28
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