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Question
The mean of 15 observations is 8. If the mean of the first eight observations is 7 and that of the last eight observations is 10, then the value of the 8th observation is _____.
Options:
A .  16
B .  15
C .  14
D .  13
Answer: Option A
:
A
We know that,
Mean = SumofallobservationsNumberofobservations
Sum of values of all the observations
=Mean×Numberofobservation
=15×8
=120
So, sum of thefirst eight observations
=Mean×Numberofobservation
=7×8
=56
Sum of the last eight observations
=Mean×Numberofobservation
=10×8
=80

Hence, value of the8thobservation
=(80+56)120
=16

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