- (5 min) Mental Math
- 38% of $1 is how much? [38 cents]
- 100% of $1 is how much? [All of it = $1]
- 138% of $1 is how much? [$1.38]
- 138% of $10 is how much? [$13.80]
- Find 30% of 40, then add 25 [37]

- (5 min) Review of selected problems from previous lesson (no more
than 3 problems)

- Hand out the Fractions, Decimals, and Percents reference sheet.
Review how to convert decimals to percents and back by moving the decimal
point.

- Setting up and solving Percent problems
When you have to solve a problem involving percents:
- Write down this equation: D x N = A

D is the percent, changed into a decimal

N is the amount you are working on

A is the answer. It can be larger than N if D is larger than 1 (100%) - If you are given a percent, change it to a decimal (D)
- Figure out whether you are missing D, N or A
- Put the other two that you have into the equation
- Solve for the missing number
- Convert D back to a percent if that was what you are asked for
- REMEMBER:
*of*means multiply and*is*means "="

- EXAMPLE 1--Find the answer: What is 8% of 752?

Well, D = .08 and N = 752 and A is the missing number, so

.08 x 752 = A

A = 60.16

- EXAMPLE 2--Find the percent: 64 is what percent of 512?

Here you are given the answer and must find the percent:

D is the missing number, N = 512 and A = 64

D x 512 = 64

D = 64/512 = .125 or 12.5%

- EXAMPLE 3--Find the "mystery" number: 125% of what number is
15?

D = 1.25, N is the missing number, and A = 15

1.25 x N = 15 N = 15/1.25 = 12

Does this seem reasonable? Yes! We are told 15 is more than 100% of the number, so the number must be smaller than 15.

- Write down this equation: D x N = A
- Extending the concept
*Discount*means you*subtract*a percent from the original amount.- If a $100 bicycle is discounted 25%, how much do you pay? [$75]
- If Lamont's has a 30% off sale, how much do you pay for $30 shoes? [$21] Not 20, that would be 1/3 off.

*Tax or interest*means you add a precent to the original amount. You pay tax after you take any discounts.- If you buy a $100 bicycle with 8.2% tax, how much do you pay? [$108.20]
- If you borrow $100 at 5% interest, how much do you have to pay back? [$105] This is called simple interest.

*Interest*is charged over time. If you borrow $100 for 2 years at 5% interest per year, how much do you have to pay back? Well, the first year you owe $105. The second year you owe $105 + 5% of 105, or $5.25. So after 2 years you owe$110.25. This is called*compound*interest. This mounts up after a long time with big loans. If your parents borrowed $100,000 for a house at 5% interest for 30 years, they would have to pay back $193,255 in all!

- (Remainder of class) In-class exercise

- Hand out homework as students successfully complete the in-class exercise.