1. SETTING UP and SOLVING RATIOS AND PROPORTIONS

2. Ratio – Comparison of 2 numbers by division.
Example: 1:2, ½, 1 to 2
Proportion – An equation stating that 2 ratios are equal.
Example: a:b = c:d

3. Example
Which of the following pairs of ratios do not form a proportion? Which ones do?
Cross
Multiply
Yes
Yes
Not a
proportion
Yes

4. Set up and solve this proportion.
8) 5 is to 4 as 45 is to x. 5
Now cross
multiply 45
____ = ____ 4 x 5x =
180 5 5 x = 36

5. First - Set up & solve the proportion.
9) 3 is to 2 as x is to 18. 3
Now cross
multiply x
____ = ____ 2 18 2x = 54 2 2 x = 27

6. NO set up this time!!
Just solve…..
10) 6x =
144 6 6 x = 24

7. You try it!!
11)
Now
Reduce
16m = 8 16 16 m =

8. 12) Mr. Jones has taken a survey of college students and found that 40 out of 47 students are liberal arts majors. If a college has 10,827 students, what is the number of students who are liberal arts majors, rounded to the nearest whole number?
First – Set up
Your proportion! 40 x
____ = _______ 47
10,827
47x =
433,080
Now cross
multiply 47 47 x =
9214

9. 13) Geothermal energy is heat from inside the earth
13) Geothermal energy is heat from inside the earth. Underground temperatures generally increase 9°C for every 300 meters of depth. How deep would a well have to be for the temperature to reach 216°C ?
First – Set up
Your proportion! 9°
216°
____ = _____
300 m 9m =
64800 9 9 m =
7200

10. 1cm 11cm 30km x 1x = 330 x = 330 km ____ = _____
14) A map has a scale of 1 cm = 30 km. If two cities are 11 cm apart on the map, what is the actual distance between the two cities to the nearest tenth of a km?
First – Set up
Your proportion!
1cm
11cm
____ = _____
30km x 1x =
330 x =
330 km