Why is 42.300 equal to 42.3

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

If the ratio of sum of the first m and n terms of an ap is m2 : n2 , show that the ratio of its mth and nth terms is (2m − 1) : (2n − 1).

Find the magnitude, correct to two decimal places, made by each of the following with positive direction of the x axis a) y= x the answer is 45° but i don’t know how