Conditional formatting to highlight a ratio of 1:3 or higher

I’m looking to use conditional formatting to highlight a ratio of 1:3 or higher to me. In the attached speadsheet, I have 3 possible instances across 4 accounts. If the ratio of instances 2 and 3 is higher than 1:3 for a particular account then I need to be able to see this quickly in red. Likewise if the instance is equal to or lower than 1:3 then I want the ratio to be highlighted green.

I thought this may be a simple case of using >= than 1:3. But this just highlighted all the ratios.

The heart of the problem is that your ratios in Column E are text strings rather than numerical values -- so a 'greater than' or 'less than' using those ratios will fail.

You can mimic the formula from cell E2 in your conditional formatting as a workaround:

=(C2/GCD(C2,D2))/(D2/GCD(C2,D2))>=(1/3)

However, you have a secondary problem, I think. 1:0 is undefined...so I don't know whether you want it green or red...so...I didn't do anything with it...

I applied the formatting to my main sheet and it did the trick. I am seeing the 1:0 issue you mentioned, but these scenarios happen so rarely in my sheet that it's not really an issue. Thanks eibi!