Transcript RATIOS & PROPORTIONS

RATIOS & PROPORTIONS
By: Ms. D. Kritikos
A ratio is a comparison of
the numbers of two sets.
Ratio of
‘s to
‘s.
3
5
3 to 5
Ratio of
5 to 3
‘s to
‘s.
5
3
In the following problems,
express the ratio of the
number of the first set to
the number of the second
set in two ways: as a ratio
and as a fraction.
PRACTICE PROBLEMS:
SET #1
1. ( ,
)
SET #2
(*,
, )
2
3
2 to 3
2. (Jim, John)
(Jo, Sue, Ann, Kay)
2 to 4 OR
1 to 2
2 1

4 2
Ratios can be reduced just like fractions.
PRACTICE PROBLEMS:
SET #1
3. (1, 2, 3, 4)
SET #2
(a, b, c)
4 to 3
4. (Bob, Dick, Al)
3 to 3 OR
1 to 1
4
3
(1st, 2nd, 3rd)
3 1

3 1
PRACTICE PROBLEMS:
(Express each as a ratio and a fraction)
5. 7 runs in 9 innings
7 to 9
7
9
6. 3 teachers for 72 students
3 to 72 OR
1 to 24
3
1

72 24
7. 6 goals for 9 shots
6 to 9 OR
2 to 3
6 2

9 3
A proportion expresses
the equality of two rates.
2 4 is a proportion because

3 6
2  6  3 4 is true.
12 is equal to 12
Remember to cross multiply.
5 3 is not a proportion because

8 4
5  4  8  3 is false.
20 is not equal to 24
Practice Problems:
(State if a proportion and explain why or why not.)
4 7 Is not a proportion because

5 8
4  8  5  7 is false.
32 does not equal 35
3 9 is a proportion because

4 12
312  4  9 is true.
36 equals 36
How to solve proportions
EXAMPLE#1:
5 15

8 n
5 n  8 15
EXAMPLE#2:
Cross
multiply
2 n

3 24
2  24  3 n
5n=120
48=3n
n=24
16=n
Practice Problems:
Problem#1:
5 6

n 24
5  24  n  6
Problem#2:
Cross
multiply
n 20

6 24
n  24  6  20
120=6n
24n=120
20=n
n=5
It’s your turn now…
to practice on the
worksheet.