7.1 ratio + proportion.notebook
January 06, 2017
1/6/17 - Warm Up Problem
Write the ratio of the first measurement to the second
measurement.
diameter of a toy car tire: 18 mm
1.
diameter of a car tire: 40 cm
2. height of a toy car: 4 ft 8 in
height of a car: 3 in
7.1 ratio + proportion.notebook
January 06, 2017
Section 7.1 - Ratios and Proportions
Goals: write and solve proportions
Tony can drive 170 miles in 2.5 hours. If he stays at the
same speed, how far will he be able to drive in 4 hours?
7.1 ratio + proportion.notebook
January 06, 2017
Proportion: an equation stating that two ratios are equal
Example:
Parts of a Proportion
Extremes: the first and last numbers in a proportion
Means: the middle two numbers in a proportion
3 6 =
4 8
7.1 ratio + proportion.notebook
January 06, 2017
Cross Products Property
If , then
Cross Multiplying
Solving a proportion means finding the value of the variable
that
makes the proportion true by finding the cross products.
Do this one in your notes.
3 x =
5 75
4 = x 6 18
6x = 72
x = 12
7.1 ratio + proportion.notebook
January 06, 2017
Solving Multi-Step Proportions
• cross multiply
• use distributive property when one of the means or extremes has two terms
Do this one in your notes.
5x + 5 = 6x - 9
-5x
-5x
5= x-9
+9
+9
14 = x
7.1 ratio + proportion.notebook
January 06, 2017
Write and Solve a Proportion
Proportions are used in many different situations...
- comparing rates
- comparing prices
- exchanging currency
- reading maps
- making scale models
Hamburger patties are on sale for $3.99 for 4 burgers.
You need 22 burgers for a cook-out. How much will you
be spending?
Currently, one Canadian dollar = 0.74 US dollars. If you
buy a pair of shoes on vacation in Quebec that cost 150
Canadian dollars, how much did you spend in US
dollars?
7.1 ratio + proportion.notebook
January 06, 2017
Write and Solve a Proportion
When making the movie Star Wars: Return of the Jedi, a model was used to film the external scenes of the 2nd Death Star. A life­
sized Death Star would have a diameter of 160 km. The model was built using about a 7 cm = 8 km scale. What was the size of the model?
7.1 ratio + proportion.notebook
Assignment:
pg. 436
(17-26) Show your work!
(40-44)
January 06, 2017