In a high school the ratio of make to female is 8: 5, when 400 senior males are removed and 300 senior females are removed, the ratio is 8: 3. the number of students in the whole school is

Male to female is 8:5

So

Let's make male = 8x

female = 5x

8x-400/5x-300=8/3
The 8/3 is because that is what the ratio was after some of the students left

multiply by 5x-300 on both sides

8x-400=(5x-300)*(8/3)

multiply by 3 on both sides to remove the denominator

(8x-400)*3=(5x-300)*8

24x-1200=40x-2400

+2400        +2400

24x+1200=40x
-24x             -24x

1200=16x

divide by 16

1200/16=16x/16

75=x

Now to find total we do 8x+5x  we said male were 8x and female were 5x

8(75)+5(75)

600+375=975 total students