7.4D Review

To find a percentage of a whole, multiply the percent (written as a decimal) by the whole. Remember, to convert a percent to a decimal, divide the percent by 100.

percent (as decimal) × whole = part (of whole)

Example: Summer bought $55.60 of clothes before sales tax. If sales tax is 7.5%, how much did she pay in taxes? How much did she spend overall?

Step 1: Convert your percent to a decimal

7.5% written as a decimal is 0.075.

Step 2: Calculate the percentage of a whole (find the amount of sales tax)

0.075 × $55.60 = $4.17

Now, to solve the second part of the question, add the sales tax to the cost of the clothes.

$55.60 + $4.17 = $59.77

So, Summer spent $59.77 with tax included.

To find percent increase or decrease, divide the change in amount by the original amount. Then convert your answer to a percent.

Change in amount = Greater value - Lesser value

percent (as decimal) = change in amount ÷ original amount

Example: A company had 125 employees on February 1. Three months later, the company had 105 employees. What was the percent decrease in the number of employees at the company?

Step 1: Calculate change in amount (greater value - lesser value)

125 − 105 = 20

Step 2: Calculate percent of change by dividing the change in amount by the original number of employees.

20 ÷ 125 = 0.16

Step 3: Convert your decimal to a percent

0.16 written as a percent is 16%.

So, the number of employees at the company decreased by 16%.

Often times you will be asked questions like the following: "A fish makes 480 dives in 10 hours. At this rate, how many dives did the fish do in 4 hours?"

When asked questions like the one above you can either:

1. Calculate Unit Rate

2. Use one of the three proportional relationship methods to solve (horizontal, vertical, cross multiplication).

Using Unit Rate to solve the following problem...
"A fish makes 480 dives in 10 hours. At this rate, how many dives did the fish do in 4 hours?"

Step 1: Set up your ratios (y/x)

Use one of the three proportional relationship methods to solve the following problem...
"A fish makes 480 dives in 10 hours. At this rate, how many dives did the fish do in 4 hours?"

Step 1: Write the rates you are comparing (make sure your units are on the same side dives in numerator ; hrs in denominator)