4.4 Adding and multiplying percents
It’s the sale season, and you are busy strolling around the mall, looking for a new pair of running shoes. Luckily, you came across a 35 percent off your favorite brand of shoes. You couldn’t calculate the price in your head so you just brought out your phone and looked up the free percent calculator.
Knowing how to compute for the percent of a certain value is quite handy. It’s applicable in all sorts of things, like computing the price for discounted items, knowing how much water your food contains, and understanding data shown on TV. Wouldn’t it be cool if you know how to compute for percentage mentally instead of just using an app?
In this chapter, we will be learning all about percent. First, we will be learning how to represent percent. We will learn how to represent them by using grids and diagrams. It’s easy to represent percent using grids. After the first part of this chapter, you will now know how to represent percent on a grid paper.
In the second part of this chapter, we will learn more on how to convert among percent, fraction and decimals. Percent, fraction and decimals can be converted interchangeably among each other, like you can convert 25 percent to .25 in decimals and ¼ in fractions.
Then, we will also be learning how to compute for the percent of a certain number in the third section, like how much is 55% of 651, or 20 2/3% of 79, or 20.6% of 1231 without ever needing to use a calculator.
For the last section, we will be discussing on how to combine percents, through adding or multiplying them. We will learn how to solve word problems that involve combined percents.
This is how percentages can be written in the form of decimal and fraction:
Percentage 
Decimal 
Fraction 
5% 
0.05 
1/20 
10% 
0.10 
1/10 
15% 
0.15 
3/20 
20% 
0.20 
1/5 
25% 
0.25 
¼ 
30% 
0.30 
3/10 
Adding and multiplying percents
Basic concepts:
 Applications of percents
 Percents, fractions, and decimals
Lessons

2.
When Kim was in grade 5, she was 130 cm tall. In grade 6, she was 20% taller than last year. In grade 7, her height has increased by 15%.