Download Unit 2 Help for Parents

Unit 2: Ratios and Proportions
How do you write ratios and equivalent ratios?
ratio – a comparison of 2 numbers using division ex: ***$$$$$ ratio of * to $ is 3 to 5 or 3:5 or 3/5
equivalent ratio – ratios that are equal
ex: 1:2 = 4:8
5 = ____ Since you must multiply 15 by 4 to get to 60, you must multiply the numerator by 4 to find
15
60
the missing number. 5 x 4 = 20 so 5/15 = 20/60
practice websites:
ratios - http://www.softschools.com/math/ratios/ratio_coloring_game/
equivalent ratios - http://www.arcademics.com/games/ratio-blaster/ratio-blaster.html
How do you write rates and calculate unit rates and prices?
rate – a ratio that compares 2 different units
unit rate – a rate with a denominator of 1
unit price – a unit rate with money
ex: 84 miles in 2 hours
ex: 42 miles in 1 hour
ex: $2.19 for 1 gallon of gas
To find a unit rate or price, divide the numerator by the denominator to get a denominator of 1.
12 oz = _____
 12 ÷ 3 = 4 so the unit rate would be 4 oz for $1
$3
$1
How do you write and solve proportions?
proportion – an equation that shows 2 ratios are equivalent
ex: 2/3 = 8/12
To solve a proportion, find the value of the missing part. You can use equivalent fractions as outlined above or you can
use cross products. To use cross products, multiply the numerator by the opposite denominator on each side of the
equal sign. Set the expressions equal to each other and solve for the missing number.
3
= 6
3·x=6·4
3x = 24 To solve for x, divide 24 by 3. 24 ÷ 3 = 8 so x = 8
4
x
practice websites:
http://www.mathplayground.com/ASB_DirtBikeProportions.html
How do you find percent of a number?
percent – a ratio that compares a number to 100
- To write a percent as a decimal: divide the value by 100
SHORTCUT: Move the decimal 2 places left
Ex:
43%  43 ÷ 100 = 0.43
85%  85 ÷ 100 = 0.85
- To write a percent as a fraction: Rewrite the percent using a denominator of 100. Simplify if possible.
Ex:
43%  43/100
85%  85/100 = 17/20
- To write a decimal as percent: multiply the decimal by 100 SHORTCUT: Move the decimal 2 places right
Ex:
0.56  0.56 x 100 = 56%
0.39  0.39 x 100 = 39%
- To write a fraction as a percent: Use equivalent fraction rules to change the denominator to 100 then write the
numerator as a percent. If the denominator is not a factor of 100, divide the numerator by the denominator to change
the number to a decimal, then follow the rules above to change the decimal to a percent.
Ex: 3/20  3/20 = 15/100 = 15%
5/8  5 ÷ 8 = 0.625 0.625 x 100 = 62.5 = 62.5%
Unit 2: Ratios and Proportions
In math, the word “of” means multiply. When you have to find the percent of a number, you need to change the
percent to a fraction or decimal and then multiply.
Example: Find 40% of 80
Method 1: Fractions
Method 2: Decimals
40% = 40/100
40 x 80 =
100
1
40% = 0.40
0.40 x 80 = 32.0
3200 =
100
32