Percent is a latin word which means per hundred or number out of 100. A percent can be represented as a fraction with a denominator of 100, or as a decimal.
For example, 65% = 65/100 = 0.65
Concept of Percentage Increases
When a number is doubled, it is increased by 100%, not 200%, but the resulting number is 200% of the original number (and the original number is 50% of the resulting number).
For example, if the price of laptop computer increases from $300 to $600 over 10 years, the percent increase is 100% because the amount increased by $300. $600 is 200% of $300 (and $300 is 50% of $600).
Similarly, when a number is tripled, it is increased by 200%, and the resulting number is 300% of the original number.
Fractions and Percentages
Percent Changes as Multipliers
Type 1: X% of a number
What is 40% of $300? The multiplier in this case is the percent as a decimal. 40% as a decimal is 0.40, and $300(0.40) = $120, so $120 is 40% of $300.
Type 2: An X% increase or decrease
A person gets 20% increase in salary of $300. What will be his new salary? In this case, the multiplier is 1 + (the percent as a decimal). Thus, $300(1.20) = $360, so that’s the amount person will get after 20% salary increase. In case of decrease, the multiplier will be 1 - (the percent as a decimal).