Question

Find the mean of 25 numbers if the mean of 15 of them is 18 and the mean of the remaining numbers is 13.

Answer 1

Mean of 15 numbers = 18
Mean of the remaining 10 numbers = 13
Sum of 15 numbers = $15\times 18=270$
Sum of the remaining 10 numbers = $10\times 13=130$
Thus, we have:
$\mathrm{Mean}\mathrm{of}25\mathrm{numbers}=\frac{270+130}{25}=16$