Aclass has less than 30 students
exactly 3/4 of them own footballs
exactly 7/8 of them own football boots.
i)how many students are there in the class?
ii)how many students own both football boots and footballs?

A class has LESS THAN 30 students 
we must find what number is less than 30 and divides into both 4 and 8 so that we don't have a fraction of a student owning a football boot
the class could have 8 students
the class could have 16 students
the class could have 24 students
lets assume that the class has the max possible so 
24 in the class

so we must find a coommon denomenator (bottom number) to keep the fractions the same we must multiply it by 1 or (number)/(same number as on top) or 1/1
so 3/4 times 2/2=6/8
7/8
so we must assume that the ones who own footballs also have boots (and not some other random person) so 
6/8 or 3/4 of the class owns both football boots so 
3/4 times 24=18
18 students own football boots

The answer is part a: use