Andrei's Percent

Percent is another way of writing a ratio when the second term of the ratio is 100.  Percent comes from the Latin words pars per centum meaning parts per hundred. We use % to express percent.

Example:
18/100 = 18%

25/100 = 25%

 If the denominator is not 100,  multiply the numerator and the denominator with the same number which will make the denominator equal to 100.

Example:

4/5 =4/5 x 20/20 = 80/100  or 80%

1/2 = 1/2 x 50/50 = 50/100 or 50%   means half of whole

1/10 = 1/10 x 10/10 = 10/100 or 10%  means 1 part of a whole

1/4 = 1/4 x 25/25 = 25/ 100 or 25%  means quarter of a whole

3. Converting Percent to Decimal to Fraction

Fraction to  Decimal  to  Percent 3/40         =     0.075   =    7.5% to decimal divide 3/40 = .075 to percent move the decimal point 2 places to the right and add the percent % sign 0.075 = 7.5% Decimal  to Percent to  Fraction 0.0064     =   0.64%      =  0.0064/10000  or       4/625                                                               to percent move the decimal point two places to the right and add the percent sign % 0.0064 = 0.64% to fraction multiply both the top and bottom by 10 for every number after the decimal point 0.0064/1  x 10 000 /10 000 =  64/ 10 000  or 4/625 Percent to Decimal  to  Fraction 75%   =       0.75        =     75/100 or 3/4 to decimal move the decimal point 2 places to the left and remove the % sign 75% = 0.75 to fraction 75/100 = 3/4 4. Finding Percent of  a number     solve:                                                                    a. 20% of 60       Mental Math                                                                   Calculator       100% of 60 is 60                                                          convert 20% to decimal       10% of 60 is 6                                                               20%  is 0.20        20% is 10% + 10%                                                      multiply 0.20 by 60        10% + 10% = 6 + 6                                                      0.20 x 60 = 12         20% = 12    b.  0.1%          Mental Math                                                                Calculator        100% of 40 is  40                                                        convert 0.1% to decimal        10% of 40 is  4                                                             0.1% is .001        1% of 40 is  0.4                                                            multiply .001 by 40         0.1% of 40 is  0 .04                                                     0.001 x 40 = 0.04         0.1 % of 40  = 0 .04    c.  250% of 400        Mental Math                                                                 Calculator        100% of 400  is 400                                                    convert 250% to decimal        50% of 400 is 200 ( 400/2)                                         250%  is 2.50        250% is 100% + 100% + 50%                                   multiply 2.50 by 400        100% + 100% + 50% =  400 + 400 + 200                2.50 x 400 = 1000        250% of 400  = 1000 5. Combining Percents    * Discount is  a deduction from the usual cost of something.    * Sale Price is the price of a good service that is being offered at a discount.    * Total price with taxes is the total amount and tax charges for all items being purchased. Example:     * A herd of caribou was moved to a new location.  The population increased by 10% the first       year and then increased by 20% the second year.       a.  Find the population after the second year.       b.  Explain why there was not 30% increase in population over  two years.     Solution:          a.  Population of caribou is 100            increase in first year    is  10%                  10%  of 100   or  0.10  x 100 = 10            population of caribou after one year is 100 + 10 = 110           New population of caribou ( after one year)  is 110            increase  in second year is  20%                    20% of 110 or  0.20  x  110 = 22            population of caribou after second year is 110 + 22 = 132                             b.  There was not a 30% increase in population over two years because after a year, the              population increased by 10% , it became 110 and this new population was increased               by 20% which gave a total population of 132 caribou after the second year.              If population was increased by 30% over two years,  the original population 100 will be               increased by 30%  which will result to 130 population. *Show you know*      What is the final price at each store.  Which is the better buy?   Explain your thinking.       Store A:  50% one day only       Store B:  25% off one day, followed by 25% off the reduced price the second day.      Example:      Store A :  50% of $200 (one day only)                       0.50 x 200 = 100     Find the discount price:                       200 - 100 = 100     The discount price is $100.     Store B:  25% discount of $200 on the first day                     0.25 x 200 = 50      Find the discount price                      $200 - 50 = 150      The discount price after the first day is $150.            The discount  on the sale price the second day is  25% of $150.                    0.25 x 150 = 37.5       Find the discount price:                    $150 - 37.5 = $112.50        The final discount price after the second day is $ 112.50.      *** Store A gives the better buy than store B.  The 25% discount followed by another 25%            is not the same as 50% discount from the original price because the discount on the             second day is only 25% of  $150 and not 25% of $200.       The original price is $200.  The selling price after two 25% discount is $112.50                    $200 - $112.50 = $87.50                    $87.50 ÷ 200 = 0.4375  or  0.44  which is 44%         ***  The total discount offered by store B is 44% which is less than 50% discount offered             by Store A, therefore Store A gives the better buy.            Video that will help us understand how to find a percent of a number.