Question

For how many pairs of positive integers (x,y) is x+3y=100?

Answer 1

It may be infinite
if we put value of y = 0,1,2,3,4 .........
x +3X0 =100
x = 100

x +3X1 = 100
x = 100- 3
x = 97
or so on...

Answer 2

33 possible positive integers are here.