First use the percent proportion to calculate the new price of the T-shirt.
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Practice makes perfect
By making a four-step solving plan we want to find how much change we get when we buy a T-shirt and pay with a $10 bill. To use the four-step solving plan we need to Understand, Plan, Solve, and Check our solution to the exercise.
Understand
We are given the regular price of the T-shirt and are told that it is on sale. Also we learn that a sales tax is added to the price. We need to calculate the final price of the T-shirt. The difference between $ 10 and the final price is the change we receive.
Plan
The regular price is $9.99 and it is on sale for 15 % off. The new price is 100 % - 15 % = 85 % of the regular price. To find the new price we use the percent proportion.
a/b=p/100
When we know the new price we have to find how much the 6 % sales tax equals. For this we will again use the percent proportion. We then subtract the sum of the new price and the sales tax from 10 to find how much change we get back.
Solve
The percent proportion states a relationship between the part a, the whole b, and the proportion in percent.
a/b=p/100
We know that the new price is 85 % of the regular price, $ 9.99. Let's calculate how much the T-shirt cost without the sales tax.
By adding the sales tax to the new price we find how much we have to pay for the T-shirt.
8.49 + 0.51 = 9.00
We have to pay $ 9 for the T-shirt. If we give the cashier a $ 10 bill, we will receive $10-$9=$1 change.
Check
We now want to check our solution. The regular price is about $10. We then got 15 % off because it was on sale.
15 % of 10 =1.5
The discount was about $1.50. The new price is the regular price minus the discount.
$ 10 - $ 1.50 = $ 8.50
With a sales tax of 6 % added to that we can calculate the final price as 100 % + 6 % = 106 % of $8.50.
Let's use the percent proportion in which we substitute b= 8.50 and p= 106 into the formula and then solve for a.
