Explanation
Step -1: Finding the sum of first 10 observations.
Average of first 10 observations=4.5
∵Average=Sum of observationsNumber of observations.
∴4.5=Sum of first 10 observations10
⇒Sum of first 10 observations=4.5×10=45
Step -2: Finding the sum of remaining 30 observations.
Average of remaining 30 observations=3.5
∴3.5=Sum of remaining 30 observations30
⇒Sum of remaining 30 observations=3.5×30=105
Step -3: Finding the average of the whole group.
Sum of total 40 students=45+105=150
Number of total observations=40
Average of the whole group=15040
=154
Hence, option B is correct.
Hence, option A is correct.
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