Let the total number of students be `x`

Let A and B represent the sets of students who passed in English and Mathematics respectively.

Then, number of students passed in one or both the subjects

=  n (A`uu`  B) =  n(A) + n(B) - n(A`nn` B) =  80% of `x` + 85% of `x` -  75% of `x`

=`(80/100 x + 85/100 x - 75/100 x)` =  `90/100 x =  9/10 x`

Students who failed in both the subjects = `(x - (9x)/(10)) = x/10`

So, `x/10`=  40 of x =  400. Hence total number of students = 400.