Danielle S. Hammelef - That Figures!: A Crash Course in Math

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Once you get the hang of them, fractions really are a piece of cake. OK, so thatsnot their technical definitionyou cant exactly eat fractions. But when you eata piece of cake, its like youre eating a fraction because youre eating a partof a whole cake.

Lets look at a tasty example. To celebrate your softball teams win in a tournament,you baked 24 yummy cupcakes.

But on the morning of the victory party, you discover that your brother and his friendsate 8 of your cupcakes! Theres no time to bake more, but luckily youll still haveenough for everyone on the team.

Even so, you want to know what fraction of your original number of cupcakes you stillhave left. To get started, write the number of cupcakes you have left as the numerator .The number of cupcakes you started with is the denominator .

We can reduce this fraction by using our factoring skills. First find the greatestcommonfactor(GCF) of 16 and 24. Then divide both the numerator and denominatorbytheGCF. This will give us an equivalent fraction for in its simplest form.

Using your factoring know-how, you figure out that 8 goes into 16 and 24 equallywithout leaving any left over or remainder. In other words, the GCF for 16 and 24is 8. So if we divide both the numerator and the denominator by 8, we get:

(168)/(248) =

So you now have two-thirds the number of cupcakes that you originally hadthanksto your annoying brother and his friends.

Youre probably wondering, When will I ever need to multiply fractions? Well, recipesoftencome with ingredients listed in fractions cup, teaspoon, tablespoon,andso on. And sometimes you need to double or triple the recipe to make enough food.Multiplyingfractions helps you get this information in a snap.

Lets say youre making a marinade for a chicken dinner. Your recipe is for 4 servings,buttonight your family of 4 is hosting your cousins family of 8. If the recipecallsfor cup of lime juice, teaspoon of red pepper, and 2cups of teriyakisauce,how much of each ingredient do you need for your feast?

Youd better set a big tableyou have 12 people coming to dinner, or 3 times as manyas the recipes serving size. This means that youll need to multiply each ingredientby 3 to figure out how much youll need for 12 people.

Lets start with the cup of lime juice. To multiply fractions, you multiply thenumeratorstogether to get a new numerator, then you multiply the denominators togethertoget a new denominator. So your lime juice calculation looks like this:

3 = ?

Wait a minute! This problem doesnt have two denominators. Now what?

Remember that any whole number can be written as an improper fraction with a denominatorof 1, so 3 = . So heres how your calculation looks as an improper fraction:

cups of lime juice

To make measuring easier, lets change this into a mixed number :

cups = 1 cups

Now do the same for the other ingredients:

teaspoon of red pepper x = (1 x 3)/(4 x 1) = teaspoon red pepper

2 cups of teriyaki sauce: (first change into an improper fraction):