Which way shows how to make a ten to find 12-4

At school there are 526 students and 263 are girls about how likely is it that a randomly chosen student will be a boy

Which of the following of the following sets of side lengths could not form a triangle?

Aclassmate thinks that solving a system by graphing gives an exact answer when the lines appear to cross at a grid point, but only an approximate answer when they don't. explain why this isn't true.