The average of 30 numbers is 15. The average of the first 18 numbers is 10 and t

Question

The average of 30 numbers is 15. The average of the first 18 numbers is 10 and that of the next 11 numbers is 20. The last number is

Options:

A . 60

B . 50

C . 52

D . 56

Answer: Option B
Answer: (b)Let the last number be x. According to the question, 18 × 10 + 11 × 20 + x = 30 × 15 ⇒ 180 + 220 + x = 450 ⇒ 400 +x = 450 ⇒ x = 450 – 400 = 50

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