Thursday, September 26, 2013

Multiplying Fractions

My daughter has a riddle she loves to ask adults.

One time a mom made a pie for her four children. The first child came to her and asked for some pie. The mom said "you can have 1/4 of the pie." Then the second child came to her and asked for some pie. The mom said "of course, you can have 1/3 of the pie." Then the third child came to ask for some pie. The mom said "yes, you can have 1/2 of the pie." When the last child asked for some pie the mom said "you can have it all." Who got the most pie?

Answer: They all got the same amount.
 

Multiplying fractions can be a difficult mathematical concept to think of in terms of real life application. We multiply fractions when we want to take part of something. Here are a few examples.

One-half of a pizza is left over and three kids would like to share it. What portion of the pizza does child get? Answer: 1/2 x 1/3 = 1/6

It took 1 of a gallon of paint to paint a bedroom. A second bedroom of the same size needs to be painted, but 1/4 of it has already been painted. How much paint should be purchased? Answer: 1 gallon x 3/4 = 3/4 gallon

Here's the same problem with different numbers.

It took 2/3 of a gallon of paint to paint a bedroom. A second bedroom of the same size needs to be painted, but 1/4 of it has already been painted. How much paint should be purchased? Answer: 2/3 gallon x 3/4 = 6/12 gallon = 1/2 gallon

Here's one more example.
You want to make 1/2 of the cookie recipe which calls for 3 1/4 cups of flour. How many cups do you need? Answer: 1/2 x 13/4 = 13/8 = 1 5/8 cups


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