Question

the average of 10 number is 75 if the first 9 of them have an average of 63 find the 10th number

Answer 1

Let 'x' be the sum of first 9 numbers

So,

$\frac{x}{9} = 63$
Hence,

$x = 63 \times 9 = 567$

Let 'y' be the 10 th number

Now ,
The average of first 9 and the last number which is 10th can be represented as

$\frac{x + y}{10} = 75$
We know 'x' = 567.

$\frac{567 + y}{10} = 75$
$567 + y = 75 \times 10$

567 + y = 750

So, y = 750 - 567 = 183