Question

Mean of 10 observations (numbers) is 20. If one number is included, the mean becomes 21, the included number is ______.

विकल्प

• 431

• 31

• 231

• 131

Answer 1

Mean of 10 observations (numbers) is 20. If one number is included, the mean becomes 21, the included number is 31.

Explanation:

The sum of the initial 10 observations is 10 × 20 = 200. When one number is included, the total count becomes 11 with a mean of 21, giving a new sum of 11 × 21 = 231, so the included number is 231 − 200 = 31.