if("score" > 75, 'Good', if("score" <45 , 'Poor','Average'))

I now want to split the Average range i.e. 45-75 into 2 categories - 45-60 Below ave and 61-75 Above ave but don't know how to stipulate the ranges. 

Want something like 45-60 or >44 and <61 - How is this done?

Regards

Mark