4(2) + 3(3) + 2(7) 8 + 9 + 14 31 -------------------- = ------------ = ---- = 3.444 4 + 3 + 2 9 9From this it should be obvious that the numbers 2,3, and 7 correspond to "molecular weights" which are represented by the variable M(i), and the numbers 4,3 and 2 correspond to "number average counts", which are represented by the variable N(i).

The symbol i is just an index. For the above data we would have

M(1)=2, N(1)=4 M(2)=3, N(2)=3 M(3)=7, N(3)=2

2 2 2 4(2) + 3(3) + 2(7) 16 + 27 + 98 141 ---------------------- = ------------ = ----- = 4.548 4(2) + 3(3) + 2(7) 31 31It should be clear that M(i) and N(i) are the same as for the Number Average Molecular Weight example.

3 3 3 4(2) + 3(3) + 2(7) 32 + 81 + 686 799 ---------------------- = --------------- = --- = 5.666 2 2 2 141 141 4(2) + 3(3) + 2(7)