Classifying points within a polygon

[buckers99]

Hey Guys, new to this forum but used to using stack overflow so apologies if I mess up a little.

I have a table containing 2 variables, (X, Y), they can be any number from 0 to 100.

X	Y
20	100
1	12

I need to classify them based on if they lay within a range on a graph, a little like the soil classification triangle. I have included the example below:

I have managed to nest IF and AND functions but this does not account for the diagonal seen in boxes C, D, and E.

Here is my function :
=IF(AND(B24<=100,C24>=50),"A",IF(AND(B24<=100,C24>35),"B",IF(AND(B24<=100,C24>25),"C",IF(AND(B24<=100,C24>10),"D","E"))))

Ideally this is what the end table looks like:

20	100	A
1	5	E

etc...

Any help will be greatly received.

B

 

[buckers99]

If anyone looks back at this, I worked it out:

=IF(B1>=50,"A",IF(B1>=35,"B",IF(B1>=25,"C",IF(B1<=6,"E",IF(AND(B1>=10,B1<=20),"D",IF(AND(A1>=50,B1>=20),"D",IF(AND(A1>=50,B1>=6),"C",IF(AND(A1<50,B1>6,B1<10),IF(B1>0.08*A1+6,"D","E"),IF(AND(A1<50,B1>20,B1<25),IF(B1>0.1*A1+20,"C","D"))))))))))