Thursday, February 2, 2012

Store Discount Math

Playing store is a fun way to review and practice figuring out discounts and sales tax.   First they set up the store by finding a few items to sell, 5 dice numbered 1-9 (1 white one and 4 colored ones), and a small dry-erase marker board with markers. They also decided to swipe pretend credit cards, rather than play money. The bench became the cash register. Here's what we did. The girls took turns being the cashier or shopper. The shopper found an item she wanted to buy and brought it to the cash register. Then she rolled the five dice to find the price of the item. She arranged the 4 colored dice to create a 4-digit money amount and told that amount to the cashier who wrote the four  digits on the marker board with the decimal after the 1st two numbers. Then the shopper told her the number on the white dice showed the percent discount by adding a zero on the end. So if she rolled a 4 the discount would be 40%. Then the cashier had to do the math by figuring out the discount. She did this by figuring out what was left after the discount to make 100%. Then they multiplied the money amount by that percent to get the discounted price. So if the discount was 40%, she multiplied the price by 60%, since 40% + 60% =100%. 

After doing the discount a few times, we changed the game so the white dice would show the sales tax percent instead of the discount. So instead of adding a zero, it would be whatever number was on the dice. So if they rolled a 6, then the sales tax would be 6%. The cashier would then write it as the decimal .06 and multiply that by the price to figure out what the sales tax would be. However, to find the full price including the decimal (percent increase), they simply added a 1 to the front of the decimal (1.06) and multiplied that by the price to show the price of the item.