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Homework – Worksheet

Do Now 5/27/14

Japan’s Bullet Train is one of the world’s fastest trains. It has a top speed of 186 miles per hour! What was the train’s unit rate for the trip below?

What is a proportion?

- Two ratios, set equal to each other.
- Used to solve for a missing piece of the proportion.
- Ex: 3x
4 = 9

- Solving Proportions: http://www.youtube.com/watch?v=Uv_hPQfJE4g

Solving Proportions

- Alex makes granola to take for a healthy snack at school. Six cups of rolled oats are needed to make 9 cups of granola. If he wants to make only 5 cups of granola, how many cups of rolled oats should he use?
- Set up a proportion for the problem.
6 c oats = ___x____

9 c granola 5 c granola

“Cross Multiplication”

6 c oats= ___x_____

9 c granola5 c granola

6 * 5 = 9x

30 = 9x

30/9 = x

3 1/3 = x

He needs 3 1/3 cups of rolled oats.

How does this work?

- There are many reasons, here’s one:
- Remember the trick for comparing fractions? Just cross multiply and compare the numerators.
- If the numerators are the same, the fractions are equal. For proportions, we assume they are equal ratios and then solve for the missing number.

More Examples

Solve using cross multiplication:

6 = x 6*12 = 8x

8 12 72 = 8x

9 = x

4 = 5 4*36 = 5m

m36 144 = 5m

28.8 = m

Number Sense

- If a car travels 48 miles per hour, about how many miles does it travel in 5 hours?
- Layla can read 24 pages in 30 minutes. How can you mentally calculate the number of pages she can read in 45 minutes?
- How can you tell without solving that n is greater than 100?
45 = n

20 50

Practice

- Classwork: 13-3
- Homework: 13-4

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