Fractions
When two fractions, let's say

have different denominators b₁ ≠ b₂, we find the Least common multiple.
We list the multiples of each denominator and we find the smallest common multiple. Then we multiply each term of the fraction in order to have that common multiple as demonimator
For example

Multiples of 4: 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, etc
Multiples of 6: 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, etc
They have as common multiples: 12, 24, 36, 48, etc
The smallest is 12
4 multiplied by 3 results in 12
6 multiplied by 2 results in 12
Then we multiply each part of the fractions

Comparing 1/4 with 1/6 is the same as comparing 2/12 and 3/12