What is ratio of 15 and 75 in lowest terms?

This is all about factorising.

Firstly yo have to find the biggest number that will go into both 15 and 75.

15 goes into both 15 and 75.

Divide both numbers by 15, (15/15=1) (75/15=5)

Therefore the ratio in its lowest terms is 1:5

If you can not recognise that 15 is the highest common factor straight off then look for smaller ones each time.

e.g.

divide by 5. Ratio = 3:15

divide new ration by 3. Ratio = 1:5