Posted by Calista on Monday, January 23, 2012 at 4:38pm.
An animal shelter have 1008 cats, dogs, and rabbits. The ratio of the number of dogs to the number of cats in the animal shelter is 3:7. The ratio of the number of rabbits to the number of dogs is 2:5.
How many rabbits are there in the shelter?

Math  Steve, Monday, January 23, 2012 at 5:31pm
d:c = 3:7
r:d = 2:5
find a common multiple for d
d:c = 15:35
r:d = 6:15
r:d:c = 6:15:35
1008/(6+15+35) = 18
so, there are
6*18 = 108 rabbits
15*18 = 270 dogs
35*18 = 630 cats 
Math  Calista, Monday, January 23, 2012 at 6:11pm
could you please tell me why need find a common multiple in this solve problem math ? thanks!

Math  Calista, Monday, January 23, 2012 at 6:15pm
oh, ye. i got it. thanks for your help!