11.1 Using Mental Methods (MATH)

Some percentages are easy to find because they are simple fractions.
There are examples of these on the first page of this unit.
You can use the easy ones to work out more complicated percentages.
You can often do this quite easily. You do not always need a calculator.

Examples :

• Question :

            There are 4600 people in a sodium. 58% are males. How many is that?
         Answer: 
            100% = 4600
            58% = 50% + 10% + 2%
            50 % = 2300
            10 % = 460
            1% = 46
            58% = 2300 + 460 - (2 x 46) = 2668

• Question:

            Work Out :  a. 35% of 84      b. 49% of 230

          Answer:

            a. 100% = 84

                35% = 10% + 10% + 10% + 5%

                10% = 8.4

                5% = 4.2

                35% = (8.4 x 3) + 4.2 = 29.4

           b. 100% = 230

               49% = 10% + 10% + 10% + 10% + 5% + 4%

               10% = 4.9

               5% = 24.5

               1% = 0.49

               49% = (4.9 x 4) + 24.5 + (0.49 x 4) = 

Work this out :

• Question:

use this fact to find : a. 52% of $78          

You may check this website if you still didn't understand:
http://www.homeschoolmath.net/teaching/percent/percent_of_number_mental_math.php