Discussion

Explanation:

Mean of 100 observations = 50

Correction to be made = 40 – 50 = -10

New average, $\frac{\mathrm{50\; \times \; 100\; -\; 10}}{100}$ = 49.9

Alternately,

Since the overall sum of 100 numbers is reduced by 10 (= 50 - 40), the average reduction of each number will be 10/100 = 0.1

⇒ New average = old average – reduction = 50 – 0.1 = 49.9

Hence, option (b).

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