Any ideas why these 2 expressions (as far as I can see = exactly the same), give vastly different results:

Code:
Y = Y + (T/6)*(2*V + 2*P + 2*P + T*S);
I make the following change (introduce T in to the brackets...
Code:
Y = Y + (1/6)*(T*2*V + T*2*P + T*2*P + T*T*S);
Using the second line of code instead of the first gives a vastly different answer?

any ideas as to why? I am completely clueless