Question

if the mean of the observation:x,x+3,x+5,x+7 and x+10 is 9 then find the mean of the last three observations

Answer 1

Hello,

As we know that mean = sum of observation/Total number of observation

$\frac{x + x + 3 + x + 5 + x + 7 + x + 10}{5} = 9 \\ \\ \frac{5x + 25}{5} = 9 \\ \\ 5x + 25 = 45 \\ \\ 5x = 45 - 25 \\ \\ 5x = 20 \\ \\ x = 4$
So, the numbers are 4,7,9,11,14

Mean of last three observation

$\frac{9 + 11 + 14}{3} \\ \\ = \frac{24}{3} \\ \\ = 8$
Hope it helps you