If she has 23 fish, how many of each type does she have?

Question

Erin's aquarium, has guppies, zebrafish and goldfish. She has 3 more guppies than zebrafish and she has twice as many zebrafish as goldfish. If she has 23 fish, how many of each type does she have?

Answer 1

Let x be the number of guppies, y the number of goldfish and z the number of zebrafish.

1) x = z + 3

2) z = 2y  or  y = z/2

3) x + y + z = 23

substitute eq (1) and(2) into eq(3):

(z + 3) + (z/2) + z = 23

2.5z + 3 = 23

2.5z = 20

z = 20/2.5 = 8

using eq(1):

x = z + 3 = 8 + 3 = 11

using eq(2):

y = z/2 = 8/2 = 4

check using eq(3):

11 + 4 + 8 = 23

There are 8 zebrafish, 11 guppies and 4 goldfish.