math
posted by Kara .
2a + 7b + 17c = 31 How do you work out what a,b and c are?? any help would be appriciated

without more info, there's no way to assign a specific value to any of them.
Just pick any value for c, cay c=1
then you have
2a+7b +17 = 31
2a+7b=14
Now, you can pick a=7, and then b=0
or you can pick b=2 and then a=0
or, you can pick a = 7, and then b=4
and so on. In general, if you have three variables, you will need three separate equations which must all be satisfied to determine unique values for the variables. 
Thanks for the pointer Steve! I'll try that :)