Question

if a < b and c < d

is this valid?
a/c < b/d

Answer 1

Not necessarily,

If you use the following values:
a = 2
b = 3
c = 1
and d = 2

a < b
2 < 3
c < d
1 < 2

However:
a/c = 2/1 = 2
b/d = 3/2 = 1.5

Therefore, since 2 is greater than 1.5, I'm afraid your statement is not valid