the reason is that for and example 2/4 if you divide both the numerator (top) and the denominator (bottom) by 2 it equals 1/2. So 2 divided by 2 is 1 and 4 divided by 2 is 2 . Another example is 3/6 because 3 divided by 3 is 1 and 6 divided 3 is 2.
5/8 that's how ratio of students that will buy lunch. so in order to find number students who will buy the lunch out of 720, just multiply 720 with 5/8 ie, 720x5/8 ie 450.
