Solving Proportions Examples Page 5

An Alaskan wildlife preserve Ranger wants to figure out how many moose live in the preserve. To do this, she randomly catches and tags 50 moose and releases them. A few months later, she catches 75 moose and sees that 20 of them are tagged. Approximately how many moose live on the preserve?

In the caught sample of 75 moose, 20 were tagged. There are 50 tagged moose in the whole population. The ratio of tagged moose to total moose will be approximately equal, so we can set up a proportion of tagged to total moose:

Now, cross multiply:

or  

Finally, divide 3750 by the coefficient 20:

Since you can't have half a moose, you can round this number to 188. You can tell the Ranger that there are approximately 188 moose living on the preserve.