Simple Interest

Think: I PARTY!

I = Interest
P = Principal
R = Rate
T = Time (in years)

I = PrT

In order to find the simple interest, multiply the principal (the original amount), with the rate and time. Do NOT FORGET to move over the percent (rate) twice to calculate using a decimal.

Discount and Markup

To find the discount and markup, you do one simple operation: Multiply.

The only thing that is different is the next step: Finding the sale price vs. finding the selling price after the markup

Sale Price:
1. Multiply the original price by the percent of discount (don't forget to move the decimal over twice first!)
2. Subtract (think ¨Sale Subtract) the discount from the original price.


Markup:
1. Multiply the original price by the percent of markup (don't forget to move the decimal over twice first!!)
2. ADD (think MArkup - Multiply, Add) the markup price to the original price.

You should get a cheaper cost for the SALE price and a higher cost for the new SELLING price (after markUP).


Example:

1. A $30 sweater is 30% off. Find the sale price.

Step One: Multiply $30 by 0.30 = $9.00.
Step Two: Subtract (think SALE-SUBRACT) 30 - 9 = $21.

You save $9.00 and only pay $21 for the sweater after the discount.


Example:

2. A computer store buys a computer for $120 and markups the price by 20%. Find the new selling price.

Step One: Multiply $120 by 0.20 = 24 ($24.00)
Step Two: Add (think MArkUP - Multiply, Add) 120 + 24 = $144.

The computer store will charge $144 to the customers after the markUP.