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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
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- 56
- 52
- 60
- 50
- 56
Correct Option: D
The average of 30 numbers = 15
The average of the first 18 numbers = 10
and the average of next 11 numbers = 20
Let the last number be n.
According to the question,
18 × 10 + 11 × 20 + n = 30 × 15
⇒ 180 + 220 + n = 450
⇒ 400 + n = 450
⇒ n = 450 – 400 = 50
