2. What is a ratio?
Write a ratio for the following in as many
ways as you can:
Boys to girls
Boys to students
Girls to students
How would these change if we got a new
female student?
3. Ratio
A ratio is the comparison of two numbers
by division.
A classroom has 16 boys and 12 girls.
Also written as 16 boys , 16:12 or 16 to 12
12 girls
Generally, ratios are in lowest terms:
16 = 16/4 = 4
12 12/4 3
4. Ratio, continued
Ratios can compare two unlike things:
Joe earned $40 in five hours
The ratio is 40 dollars or 8 dollars
5 hours 1 hour
When the denominator is one, this is called
a unit rate.
5. Proportion
Proportion is a statement that says two ratios
are equal.
In an election, Damon got three votes for each two
votes that Shannon got. Damon got 72 votes. How
many votes did Shannon get?
Damon 3 = 72 so 3 x 24 = 72
Shannon 2 n 2 x 24 48
n = 48, so Shannon got 48 votes.
6. Proportion, continued
Tires cost two for $75. How much will
four tires cost?
# of tires 2 = 4 so 2 x 2 = 4 tires
cost 75 n 75 x 2 $150
n = 150, so four tires cost $150
7. Proportion, continued
One more way to solve proportions:
Cross Products
2 = 6 2 x n = 6 x 8 2n = 48
8 n 2 2
n = 24
8. Proportion, continued
Now you try!
Three cans of soup costs $5. How much
will 12 cans cost?
# of cans 3 = 12 3 x 4 = 12 cans
cost 5 n 5 x 4 20 dollars
n = 20, so 12 cans cost $20
9. Exit Slip
Write and solve a proportion for the
following:
If Marcie pays $4.80 for three pounds of
strawberries, how much will she pay for
seven pounds?
