Conditional formatting with IF function

I have a range of data and I am trying to apply conditional formatting:

Can someone please help me write the formula for;

IF (A/B) is less than 60% then the cell should be highlighted in Red
If (A/B) is between 61% to 80% then the cell should be highlighted in Yellow
and
If (A/B) is greater than 80% then the cell should be highlighted in Green