Okay, let's slightly generalize this
Average of numbers is
and then numbers are removed, and you're asked to find the sum of these numbers.
Solution:
If average of numbers is then the sum of all these numbers is
Now we remove numbers, so we're left with numbers. and their. average will be let's call this new average
For simplicity, say, sum of these numbers, which are removed is denoted by .
so the new average is
or,
Simplify the equation, and solve for to get,
Hope you understand it :)