To compute the percentage of total purchases for a given category, which formula would you use?

• A. Multiply the category count by 100
• B. Subtract the category count from the total
• C. Add the category count to the total
• D. Divide the category count by the total and format as percent

Answer: (D)

To find what share a category represents of all purchases, you form the ratio of the category’s count to the total purchases and then express that ratio as a percent. Dividing the category count by the total gives a decimal between 0 and 1, and formatting it as a percent converts it to a percentage by multiplying by 100. So the proper approach is to divide the category count by the total and format the result as a percent. For example, if the category has 40 purchases out of 200 total, 40/200 equals 0.20, which is 20%. Multiplying by 100 or adding/subtracting would not yield the correct share.