Answer:
Let's call the number of English books "E", the number of Chinese books "C", and the number of Math books "M".
We know that:
E + C = 365 (Equation 1)
E + M = 302 (Equation 2)
M = 4/7 C (Equation 3)
We can solve for one variable in terms of the others and substitute into the other equations.
Let's solve Equation 3 for C:
M = 4/7 C
C = 7/4 M
Now we can substitute this into Equation 1:
E + C = 365
E + (7/4 M) = 365
And into Equation 2:
E + M = 302
E + M = 302
Now we have two equations with two variables, E and M. We can solve for one of them and then use that to solve for the other.
Let's subtract Equation 2 from Equation 1:
E + (7/4 M) = 365
- E - M = -302
-----------------
(3/4 M) = 63
Multiply both sides by 4/3:
M = 84
Now we can use Equation 2 to solve for E:
E + M = 302
E + 84 = 302
E = 218
So there were 218 English books.