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 _____.
16
We know that,
Mean = Sum of all observationsNumber of observations
Sum of values of all the observations
=Mean×Number of observation
=15×8
=120
So, sum of the first eight observations
=Mean×Number of observation
=7×8
=56
Sum of the last eight observations
=Mean×Number of observation
=10×8
=80
Hence, value of the 8thobservation
=(80+56)−120
=16