The beautiful thing about "the unit analysis approach to math" is that it reduces so many problems in mathematics to the same strategy.

The more you practice using unit analysis, the more you will build your intuition for knowing when to multiply, when to add, when to subtract, and when to divide.

Think about this example. You are tutoring a young student who is trying to solve the following problem. "An employee at a fast-food restaurant is paid $8.50 per hour. The employee works 32 hours in a week. How much does the employee earn in the week?"

For you, it is intuitive to multiply $8.50 per hour by 32 hours. But how would you explain to a 3rd or 4th grader why you multiply?

The grizzly bear, Florida panther, and the American alligator were three of the first animals to be listed as "threatened with extinction" in 1966. Currently, there are 415 animals listed as endangered in the United States. Visit the U.S. Fish & Wildlife Service to learn more about the endangered species program and how you can help.

3. You can estimate the number of species of mammals that will become extinct during the next 100 years as follows.

   

   During the next 100 years, perhaps 15 species of mammals will become extinct.

4. You can estimate the number of years in which 40 more species of birds will have become extinct as follows.

   

So you might expect it to take about 130 years for 40 additional species of birds to become extinct. Remember, however, that this type of prediction is quite rough. It assumes that the rate of extinction of new species will be the same as it was during the past 410 years.