Question

1800 gym members 3/4 over 25 1/5 over 60 what is the remaining under 25

Answer 1

1800*3/4=1350 so their are 1350 people over the age of 25.
1800*1/5=360 so their are 360 people over the age of 60.
so if their are already 1710 people(1350+360). 
So 1800-1710=
90 People under 25.