Your college marked like that? That's just bad marking criteria. Over here, if you can show that you understand the concept, you've got at least half marks. Even if you screw up a sign, number or operation, and continue the equation how your supposed to, then you will generally get 4/5 or 3/5, because it was a small error. Which is how it should be. Get the general solution right, then focus on the specifics. True in any case.
Now, I am off to study for maths, preparing myself for a fail mark and preparing some entertaining quotes to write when I run out of answers I can get to entertain the markers. Like how trees are being used for slave labor to make paper, how they're getting paid 20c an hour, and how the ents will find out and enslave the human race for the atrocities the humans made the trees suffer, and how they will eventually hook us up to giant structures and feed off our life force while we undergo simulations of everyday life.
Thats right. The forests are the machines!!!