Understanding proportion
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Transcript of Understanding proportion
Understanding Proportion
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
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.
Ratio, continued
Let’s look at a classroom:Ratios can be part-to-part
16 boys15 girls
Ratios can be part-to-whole16 boys
31 students
Ratio, continued
If a ratio is part-to-whole, you can divide and find a decimal or a percent.
16 boys31 students
31/16.00 = .516, or 51.6% are boys
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.
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
Proportion, continued
One more way to solve proportions:
2 = 6 2 x n = 6 x 8 2n = 488 n 2 2
n = 24
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