Question

If 30% of John's photographs were perfect, but 210 photographs were not perfect, then how many photographs were there in all?

Answer 1

If 30% were perfect, 70% were not perfect.  So we know that 70% of the total number of photographs is 210.

p(70/100)=210  multiply both sides by 100

70p=21000  divide both sides by 70

p=300

So there are 300 photographs in all.