Complex IF Formula

for cell D11 ...

=if(and(A10>=4,A10<=12,B10="Y",C10="Y"),if(and(A11>=4,A11<=8,C11="Y"),"aa",if(and(A11>=1,A11<=3.5,C11="Y"),"bb",if(and(A11>=1,A11<=3.5,C11="Z"),"cc"))),"")

Will test and respond. Much thanks for such a quick response.

Thank you rcm. It works perfectly. However I now realize I left out one line that I have added below. It is the 2nd line.

IF A5 is any number from 4.0 thru 12.0, AND IF B5 is Y AND C5 is Y, THEN IF A6 is any number from 4.0 thru 8.0 AND C6 is Y, then D6 = aa

IF A5 is any number from 4.0 thru 12.0, AND IF B5 is Y AND C5 is Y, THEN IF A6 is any number from 4.0 thru 8.0 AND C6 is Z, then D6 = dd

However, with the same criteria for A5, B5 and C5, IF A6 is any number from 1.0 thru 3.5 AND C6 is Y, then D6 = bb
AND with the same criteria for A5, B5 and C5, IF A6 is any number from 1.0 thru 3.5 AND C6 is Z, then D6 = cc

All A column cells are numbers from -30.0 thru 30.0. All B and C column cells are either a "Y" or a "Z".