Question 547534
x+y=13


5x+8y=1000

8y=1000-5x
y=125-5/8 x

y has to be a whole number

so (5/8)x should be a whole number

x should take values of multipls of 8 till y is equal to 0

5/8 * x = 125
x=8*125/5 = 200 

 
25 combinations are possible