I average about 1-2 mistakes for exam 1.
Most of my mistakes are pretty silly mistakes, and if i had checked my work thoroughly, i might have found them

Anyway, my advice would be that after you have completed your exam (that's if you have time), when you're checking your answers, instead of working the question out again in the same way, go through a process of elimination and cross out each option that is wrong. I've found that sometimes when i repeat the same question again, i'm likely to make the same mistake as i did the first time (as i'm thinking in the same way) so i find thats its more safer to use a slightly different way to check the second time, to avoid making the same mistake? Lol, i'm not good at explaining, i give up

haha
Just make sure you read the question very very carefully and check to make sure you don't jump to a conclusion straight away, further maths likes to play little tricks on you