Many percentage calculations can be done in your head. For example, 50% of 200. Since 50% is the same as or a half () we can find a half of 200 to get 100.

Other calculations can be completed on your calculator.

Step 1: change the percentage to a decimal.

Step 2: multiply this decimal by the number you want to find the percentage of.

e.g. To find % of , enter the calculation into your calculator: .

For further explanations of finding a percentage of an amount see  Khan academy.

The best way to increase an amount by a percentage is to use a one-step method.

To increase an amount by 25% we multiply by 1.25. The 1 represents the whole amount and the 0.25 represents the additional 25%.

e.g. The widget share value has increased from $2.85 by 16%. Find the new share value:

$2.85 x 1.16 = $3.306 = $3.31 (rounded to 2 decimal places).

For a further explanation of increasing by a percentage see  Khan academy.

Decreasing the value of a quantity by a percentage is also best done with a one-step method.

Think about what percentage of the quantity is left after the percentage decrease.

For example, a decrease of 20% will leave 80% of the quantity. Therefore, to find the decreased amount we multiply by 1 minus the percentage decrease (expressed as a decimal).

For example, my car’s value has decreased from $11,500 by 5%. Find the new value of the car:

$11,500 x 0.95 = $10,925.