x,y為正整數且1<x<y<42, 4/3>y/x>5/4求y/x之值(拜託請詳解)?

Sol
5/4<y/x<4/3
5x/4<y<4x/3
42*5x/4<42y<42*4y/3
52.5x<42y<56x
(1) 42y=53x
53｜y (不合)
(2) 42y=54x
y/x=54/42=9/7……………….
(3) 42y=55x
55｜y (不合)

4/3>y/x>5/4
4/3>y/x y/x>5/4
4x/3>y y>5x/4
4x/3>5x/4
16x>15x
x>0 (delete)
無解