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Math Lesson 5.1.4 - Calculating the Percentage of another Percentage of an Amount

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Welcome to our Math lesson on Calculating the Percentage of another Percentage of an Amount, this is the fourth lesson of our suite of math lessons covering the topic of Definition of Percentages, you can find links to the other lessons within this tutorial and access additional Math learning resources below this lesson.

Calculating the Percentage of another Percentage of an Amount

In this case, we have to find a compound percentage, which is calculated by multiplying the two percentages and then, the total percentage is used as the term A in the formula of the previous paragraph. Thus, we have

x% of y% of A = x/100 ×y/100 ×A = (x ×y ×A)/10,000

Let's explain this point through an example.

Example 4

A tailor has to sew 120 dresses in a month. He was able to sew only 80% of this amount and eventually take them to market. However, only 75% of the dresses were sold. How many dresses did the tailor sell during the given month?

Solution 4

The long way would imply calculating how much is 80% of 120 and then, calculate 75% of the new amount obtained. We will use this method as a proof form the short method used below.

In simple words, we have to calculate 75% of 80% of 120. Here, x = 75 and y = 80. Thus, we have

75% of 80% of A = 75/100 × 80/100 ×120
= 75 × 80 × 120/10,000
= 72 dresses

The long way:

The number of dresses the tailor sew (N1) is

N1 = y % of 120
= y/100 ×120
= 80/100 ×120
= 96 dresses

The number of dresses sold (N2) is

N2 = x % of 96
= x/100 ×96
= 75/100 ×96
= 72 dresses

As you see, the result is the same but the first method is shorter.

Obviously, percentages can also express amounts that are greater than the whole. In such cases, we have the numerator of the corresponding fraction greater than the denominator. Everything else is the same as above.

Example 5

A researcher planned to read 160 pages in one day but he stayed in library longer and read 184 pages during that day. What percent of the initial goal did he achieve?

Solution 5

We have to calculate how much percent of 160 (the initial plan or the whole) is 184. Taking 184 = A and 160 = B, yields

A = x% of B
184 = x/100 × 160
x = 184 × 100/160
= 115

Hence, 184 represents 115% of 160.

More Definition of Percentages Lessons and Learning Resources

Percentages Learning Material
Tutorial IDMath Tutorial TitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
5.1Definition of Percentages
Lesson IDMath Lesson TitleLessonVideo
Lesson
5.1.1Definition of Percentages
5.1.2Writing a Number as a Percentage of another Number
5.1.3Finding the Percentage of an Amount
5.1.4Calculating the Percentage of another Percentage of an Amount
5.1.5Operations with Percentages

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