Dear Angela
I covered this point in my book Fatty Acid and Lipid Chemistry (1996)
which I am rewriting at the present time. I think the following excerpt
will help you. You should be able to calculate the values for 3 acids.

Frank Gunstone

Triacylglycerols (triglycerides) are fully acylated derivatives of glycerol
and are the most common form of lipids. It is unusual for natural
triacylglycerols to have only one kind of fatty acid though triolein is
presents in olive and other high-oleic oils. More commonly, two or three
different fatty acids are present. The number of different triacylglycerol
molecules present in a fat rises rapidly with the number of fatty acids
present in the fat. With only two fatty acids such as palmitic and oleic a
fat can contain six different triacylglycerols though this number reduces
to four if regioisomers are ignored. These may be represented as PPP, POP
(and PPO), POO (and OPO), and OOO. The situation with more fatty acids is
set out in Table 3.6. The triacylglycerol composition of some natural oils
has been discused in Chapter 1. Hydrolysis of these molecules under enzymic
and non-enzymic conditions is discussed in Sections x and y.

Table 3.6 Relation between the number of fatty acids and the maximum
number of triacylglycerols that can be formed from them

Number of acids 5 10 20 n
Number of triacylglycerols
All isomers distinguished 125 1000 8000 n3
Excluding optical isomers
75 400 4200 (n3 +n2)/2
No isomers distinguished
35 220 1540
(n3 + 3n2 +2n)/6

Frank Gunstone
3 Dempster Court
St Andrews
Fife KY16 9EU
SCOTLAND
tel 01334 47 99 29