Let's first start off by making 2/10 the same denominator as 5/100. To do this you would need to multiply both sides of the fraction by 10. You wild end up with 20/100. Now we worry about the striped fish. There are 5/100 striped fish, since we have the same denominator we can add them together!
20+5=25
25/100 is reduced to 1/4!