(Original post by Lil-Lele)
Thank you, how about if I got 50% today? rather than 40%?
The formula you are looking at is 0.3 times your mark today plus 0.7 times your mark in the next exam gives you your total mark. You can rearrange this for whatever variable most concerns you, or if you put it into Wolfram Alpha in the form I linked you to it will just tell you. In this instance, the formulation would be 0.3 * 50 + 0.7 * k = 60, where 50 is your mark today, k is your mark next time and 60 is the mark you hope to get overall. Solving for k will answer your question now, and swapping numbers for variables will answer any other questions you may have.