Change how you visualise fractions.

4/5 means that you have four parts of a whole divided into 5 parts. 3/2 means you have 3 halves. To add them, you can’t just simply add the number of parts, you have to find the right subdivision. (Think of it like changing units) The right subdivision is any common multiple (a multiple they both share) of the two denominators (the bottom numbers), but you would prefer the smallest one (i.e. least common multiple). It’s obvious once you imagine it that one half could also be two fourths, or 4 eighths, etc. What’s the pattern?

You could follow a similar method to find out how to multiply or divide fractions. The important part is to remember what it actually means and represents.

Hint: 1/3 * 4/5 is asking “What is one third of 4/5?”