I am having an issue with an IF formula that contains 4 nested arguments....

Hello everyone....
Nub here to the forums that has an average amount of experience with Excel(Read dangerous....). I have a spreadsheet that contains the following =IF formula......

=IF(C24<750,"Class C", IF(C24<900,"Class B", IF(C24<1200,"Class A",IF(C24>1199,"Class AA"))))

Everything works great with the formula, but I am trying to add a criteria to this part of the argument... IF(C24>1199,"Class AA". As it stands, each nest is evaluating one particular cell within the sheet. For the 4th argument, I want it to only return the value "Class AA" if another cell C11 also meets a criteria. For example, here is what I tried adding...... IF(C24>1199&C11>=1300,"Class AA" . My hope was that any value in C24 above a 900 would return "Class A", unless it was 1200 or greater AND C11 was 1300 or greater. If those two criteria were met, then it would return "Class AA". Here are a couple of more examples of what I am trying to obtain.....

C24=925/C11=1100. Returns "Class A"
C24=1200/C11=1550. Returns "Class AA"
C24=1300/C11=1200. Returns "Class A"

I appreciate any help or suggestions! Thanks everyone for your time.....

Hello Dred and Tony...
Thank you both for your replies. Both solutions worked with one exception. If C11 contained a value that would normally trigger a "Class AA" but C24 didn't; the formula correctly returned a "Class A" result. If you flip-flop the result, whereas C24 contained the value that would normally trigger the "Class AA" result but C11 didn't; the result is a blank cell. The result should be a "Class A" result. Any suggestions?? Here again is the formula.......

=IF(C24<750,"Class C", IF(C24<900,"Class B", IF(C24<1200,"Class A",IF(AND(C24>1199,C11>1300),"Class AA",""))))

Tony that did it! Thanks again for your help. You too Dred!