The Math of Back-to-

School Shopping

What you will learn

• Summary

• In this issue of Math in the News we look at the prices and purchases parents and teachers make during back-to-school shopping

• Determine the price of items before and after tax by multiplying by percents and decimals.

• Compare prices in a table

School Supplies

• Every August and September, schools compile a list of supplies students will need for school.

• Basic supplies include…

• Pencils

• Paper

• Binders

• Today, kids might also need…

• A computer

• An iPad

Money-Saving Tips

• Check out this local news video on how to

save money on school supplies.

• http://newyork.cbslocal.com/2016/08/11/back-

to-school-shopping/

The Cost of School Supplies

• School supplies can add up! Especially when you include the 6% - 8% sales tax (depending on the state).

• Visit http://taxfoundation.org/article/state-and-local-sales-tax-rates-2016 to see the sales tax rate in your state!

• In the next slides, we’ll look at how to find the price of an item before and after sales tax.

What’s the total cost after

sales tax?

• When you see an item at a store and it’s marked

with a price, say $5.25, but that’s not the total cost

you pay. That’s the price BEFORE tax.

• To find the total cost of an item after sales tax,

Price + Tax = Total cost

How do you calculate the tax?

• To find the tax, multiply the cost by the sales tax

rate as a percent or a decimal:

Tax = Price x Sales Tax Rate

What is the formula for total

cost?

Total Cost = Price + Price • Sales Tax

= Price (1 + Sales Tax)

Example 1

Problem

• What is the cost of a notebook that costs $5.25 with a 6%

sales tax?

Solution

Total Cost = Price (1 + Sales Tax)

= 5.25 (1 + 0.06)

= 5.25 • 1.06

= 5.57

Example 2

Problem

• Take a look at the pre-tax price of some common back-to-school items:

• Box of 40 #2 pencils: $4.99

• Plastic Pencil Case: $2.04

• Package of lined paper: $2.54

• Package of 5 binders: $28.99

• What’s the total cost?

Source:http://www.target.com/s?category=0%7CAll%7Cmatchallpartial%7Call+categories&searchTerm=binder

Example 2

Solution

• When you have multiple items, first add all the individual

prices to find the Total Price. Calculate the tax on the Total

Price.

Total Price = 4.99 + 2.04 + 2.54 + 28.99 = 38.56

Total Cost = Total Price (1 + Sales Tax)

= 38.56 • (1 + 0.06)

= 38.56 • 1.06

= 40.87

Tax-free Holiday!

• As you can see, there’s a big difference

between the before-tax price and the after-tax

price, especially for more expensive items.

• To help families and teachers, many states

participate in a “tax-free” holiday where, for

one weekend, people shop tax-free.

• How much money would you save?

Your Turn!

• Take a look at your back to school shopping list. Make sure you include all items (clothing, electronics, school supplies, etc).

• Go to http://www.target.com/ or the website of the store you bought your supplies to find the prices.

• Go to http://taxfoundation.org/article/state-and-local-sales-tax-rates-2016 to see the sales tax rate in your state.

• Calculate the Total Price and the Total Cost.

What are the savings?

• How much more money did you spend in total

with taxes compared to without taxes?

• What do you notice about how much you pay

in sales tax as the price of an item increases?