Question

One hundred families each have $2$ fish. Each fish has either one stripe or two stripes. In total, there are $273$ stripes. How many one-striped fish are there in total?

Answer 1

Let x be the number of one-striped fish and y the number of two-striped fish.

100 families each have 2 fish, so there are a total of 200 fish:

x + y = 200

x one-striped fish carry a total of x stripes, while y two-striped fish carry a total of 2y stripes. There are 273 stripes overall, so

x + 2y = 273

Solve for x and y. Subtracting the first equation from the second eliminates x :

(x + 2y) - (x + y) = 273 - 200   ==>   y = 73

Then

x + 73 = 200   ==>   x = 127