Essential Question:
A percent equation is an equivalent form of a percent proportion in which the percent is written as a decimal.
What is the simple interest
formula?
Part = Percent Whole
What do the
variables represent?
Try one of each type:
Remember: Type
Example
Equation
Missing Part What number is 75% of 4? n = 0.75(4)
Missing Percent
3 is what percent of 4?
3 = n(4) Missing Whole 3 is 75% of what number?
3 = 0.75n Let's mix them up: Remember: Part = Percent Whole
Part = Percent Whole
Find 42% of 150.
Find the Part ­­ Find 52% of 85.
9 is what percent of 25?
Find the Percent ­­ 28 is what percent of 70?
27 is 54% of what number?
What is 37.5% of 89?
Find the Whole ­­ 18 is 45% of what number?
48 is 64% of what number?
38 is what percent of 40?
The percent equation can be used to find discounts and interest.
Manuel wants to buy a skateboard. The regular price of the skateboard is $135. Suppose it is on sale at a 25% discount. Find the sale price of the skateboard.
What is a discount??
Method 1
First, use percent equation to find 25% of 135.
Let d = discount
d = 0.25(135)
d = 33.75
Then, find the sale price by subtracting the discount from the regular price.
135.00 ­ 33.75 = 101.25
What is interest??
The sale price would be
$101.25.
Manuel wants to buy a skateboard. The regular price of the skateboard is $135. Suppose it is on sale at a 25% discount. Find the sale price of the skateboard.
Let's try another one. The regular price for a digital music player is $69. It is on sale at a 20% discount. Find the sale price of the player.
Method 2 A discount of 25% means the item will cost 100%­25% or 75% of the original price. Use the percent equation to find 75% of 135.
Do you like Method 1 or Method 2 ?
s = sale price
s = 0.75(135)
s = 101.25
The sale price would be
$101.25.
Interest is the amount of money _____ or _______ for the use of money. For a savings account, ________ is earned. For a credit card, _______ is paid.
The formula for finding interest is
Interest
I = p r t
I = p r t
Try another. Nathaniel placed $2400 in the bank for 5 years. After the 5 years, he had earned $552 from the interest. Find the annual interest rate the bank paid him.
I = p r t
Suppose Samuel invests $1200 at an annual rate of 6.5%. How long will it take to earn $195 in interest?