Jenny's Percent Post

1. How to find Key Percents

• 50% - divide the number you want to find the percentage of by 2 to get 50%
• 10% - divide the number you want to find the percentage of by 10 to get 10% 
• 1% - divide the number you want to find the percentage of by 100 to get 1%
• 25% - divide the number you want to find the percentage of by 4 to get 25%

        A percent is a fraction out of a whole.

2. Representing Percents

        Image #1
180%
+  

^100%                                               ^ 80%
        
          Image #2
12 3/4%

^ 12.75%
         Image #3
0.7% (7 out of 10)

^ 0.7%

3. Converting Decimal to Percentages to Fractions

        Percent to Decimal:
Divide the percentage by 100(move decimal two spaces forward/to the right)

        Decimal to Percent:
Multiply decimal by 100(move decimal two spaces back/to the left)

        Fraction to Decimal:
Divide the numerator by the denominator 

        Decimal to Fraction:
Multiply the number by 10 after every number after the decimal

        Fraction to Percent:
Divide the numerator by the denominator then multiply by 100

        Percent to Fraction:
Remove percentage sign, then divide by 100

• 26%

Decimal: 0.26             Fraction: 26/100

(26 x 100 = 0.26)      (26 ÷ 100 = 0.26)

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• 7/10

Decimal: 0.7          Percent: 70%

(7 ÷ 100 = 0.7)     (0.7 x 100 = 70%) 

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• 0.024

Percent: 2.4%                   Fraction: 2.4/100
(0.024 x 100 = 2.4%)      (2.4 ÷ 100 = 0.0024)

4. Percentage of a number using Mental Math and a Calculator

• 20% of 60

          v                                                              60 ÷ 10 = 6(10%)

         10% of 60 = 6                                          6 x 2 = 12(20%)

                                     = 12

         10% of 60 = 6

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• 0.1% of 40

          v                                                               40 ÷ 10 = 4(10%)

         1% of 40 = 0.4                                          4 ÷ 100 = 0.04(0.1%)

-                                    

         0.5% of 40 = 0.2

-

         0.1% of 40 = 0.04

-                                         = 0.04

         0.1% of 40 = 0.04

-

         0.1% of 40 = 0.04

-       

         0.1% of 40 = 0.04

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• 250% of 400

          v                                                   400 x 100 = 40 000

         100% of 400 = 400                       40 000 ÷ 40 = 1 000

+

         100% of 400 = 400      = 1 000

+

         50% of 400 = 200

5. Explaining Discounts, Sale Price, and Total Price with Taxes

Question #7 on page 149:
A herd of 100 caribou was moved to a new location. The population increased by 10% the first year, then increased by 20% the second year.

a) Find the population after the second year.
10(increase in the first year) ÷ 100 = 0.1        20(increase in the second year) ÷ 100 = 0.2
0.1 x 100 = 10                                                     0.2 x 110(total of first years) = 22
100 = 10 = 110(first year)                                110 + 22 = 132(second year)
                                                                                                 ^ total
b) Explain why there was not a 30% increase in population over the two years.
         A: There was not a 30% increase because if there was, it wouldn't make sense due to it would be 130 caribou in total in the end if there was the 30% increase but since it was 132 in total for the second year, it'd be confusing on how it's 132 one year and 130 the year after.

Here is a video of converting decimals to percent for anyone who has trouble (: My brother watched it and he is finally understanding how to convert a decimal to a percent just by watching this video once.