Adding percentages together for overall percentage calculator

In the course of running your business, you may find it necessary to perform calculations where you need to combine percents. Percents can be added directly together if they are taken from the same whole, which means they have the same base amount. This would be the case if you have a pie chart categorizing the expenditures in your office and wish to know the total percentage spent on office supplies and computer equipment. You would add the two percentages to find the total amount. You can use Microsoft Excel to to perform this operation.

1. Run Microsoft Excel. Open an old workbook, or create a new one.

2. Choose a cell that will contain a percentage, and type a number into it. For example, type “10” inside a cell in column A.

3. Format the number in column A so that it is a percentage. First, select the cell with the number.

4. Select the “Home” tab. Click “Format” then “Format Cells.” Select the “Number” tab, then click “Percentage” and the “Okay” button. The number in column B will change its display to a percentage. By default, Microsoft multiplies the number by 100; if necessary, modify the result so that it will display the amount, such as 10% instead of 1000%.

5. Type a different number in another cell and format it so that it is a percentage. For example, type “5” inside a cell in column B and change it to 5%.

6. Add the percentages together using the “Sum” function and display the result inside a different column. First, click on a cell in column C and click “Fx” in the formula bar. Select “Sum,” then “Ok.”

7. Fill in the text boxes next to “Number1” and “Number2.” For instance, select the cell with the percentage in column A for “Number1” and select the cell with the percentage in column B for “Number2.” Click “Ok” and the percentages will be summed. For example, if you combined "10%" and "5%" then "15%" will be displayed in column C.

The data on 4 examinations showed scores of 75 percent correct, 87 percent correct, 69 percent correct, and 93 percent correct. The overall grade was determined by taking the Arithmetic Mean (or 'average') of these scores, reporting a combined percentage of 81.

Consider that the 4 examinations had

24 correct out 32 questions for 75 percent

87 correct out of 100 questions for 87 percent

38 correct out of 55 questions for 69 percent

and 93 correct out of 100 questions for 93 percent.

Thus if the questions are of equal merit across the examinations, there are 242 questions answered correctly out of 287 for a percentage of 84.3.

Discuss the discrepancy between 81 percent and 84.3 percent for these two computations.

What is the mathematical explanation?

Another example:

30 correct out 32 questions for 94 percent

75 correct out of 100 questions for 75 percent

50 correct out of 55 questions for 91 percent

and 69 correct out of 100 questions for 69 percent.

Here, the AM = 82.3 percent whereas 224 correct out of 287 is 78 percent.

1. Add the given percentages to 100.
2. Convert the percentages to decimals.
3. Multiply to the base value.
4. Multiply the second percentage.

We’ll go through these stages in detail below.

Step 1: Add the given percentages to 100

For example, if we want to increase 300 by 10% then increase the result by 20%.

Step 2: Convert the percentages to decimals

Change the percentages to decimal by moving two decimal places to the left of the percentages.

Step 3: Multiply to the base value

Multiply the first given percentage (in decimal form) to the base value. So, for our example, we multiply 300 by 1.10.

Step 4: Multiply the second percentage

Use the new value and multiply the second percentage (also in decimal form). To find the final value, we multiply 330 by 1.20.

Examples of adding consecutive percentages together:

Q1) A store sells a pair of pants at a profit of 15%. A concessionaire also adds 5% on top of the cost. If the supplier cost of the pants is $800, how much would a customer have to pay at a concessionaire?

Add the percentage with 100 first. Hence, we have:

Move the percentages two decimal places to the left.

Now that we have the decimal forms, we first multiply 800 by 1.15.

To find the final cost, we multiply 920 by 1.05.

So, the final cost of the pants would be $966 at the concessionaire.

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