Applications of Percent

Presenter: Brett

Today we're going to talk about percent with, sales tax, tips, commission, and percent error in manufacturing.

Sales Tax

Sales tax is that awful extra amount of money you have to pay when you buy something,

Formula: Purchase price*tax rate=sales tax

Tax+Purchase price=total price

  1. ex= $132.78 bike     sales tax rate= 8%       .08*132.78=10.62      so, 132.78+10.62=$143.40

ex. $450.75 TV     Sales tax=8.5%       

ex. $13,485 car     Sales tax=11%

student ex. $53,936 car      Sales tax=35%

Estimating Tips

ex. Your family takes a taxi to the train station. The taxi fair is $17.85. Estimate a 15% tip to give to the driver.

17.85=18-Round to the nearest dollar

0.1*18=1.8-Find 10% of the bill

1/2*1.8=0.9-Find 5% of the bill. 5% is 1/2 of the 10% amount.

1.8+0.9=2.70-Add the 10% and 5% to get  15%

For a $17.85 taxi fare, a 15% tip is about$2.70

ex. estimate a 15% tip for each amount


student: $61.80

student: $49.75

Finding Commission

Some sales jobs pay you a commission, a percent of the amount of your sales. To find commission, use Commission=commission rate*sales (Hint: to turn percent into decimal, do percent/100.)

ex. Find the commission on a $500 sale with a commission rate of 12.5%.

0.125*500=62.5-write 12.5% as .125 and multiply

The commission on the sale is: $62.5o

ex. Commission on a $3200 sale with a commission of 6%

student ex: $800 purchase, with a 12% commission

A sales agent earns a weekly salary of $650, plus a commission of 4% on all sales. His sales  this week are $125o. How much does he earn?

Formula: total earnings=salary+commission



total earnings this week are:$700

ex. A real estate agent earns a weekly salary of $200, this week he sold a house for $120,000 and got a 5.5% commission. How much does he ear this week?

student ex. A car salesman earns a weekly pay of $1200, plus a commission of 5%, his sales this week are $45,876. How much does he earn this week?

Application: Percent error in Manufacturing

Quality control supervisors use percent error to assure that products meet their specifications. The formula for PERCENT ERROR uses the absolute vale of the difference between the measured value and the actual or desired value.

Percent Error= (Actual Value-Measured Value)/Actual Value*100

The supervisor at a shoelace factory checks the length of 1 shoelace out of every 500 made. If shoelaces are not within 0.5% of the specified length, they will be rejected. A 36-inch long shoelace she just checked was 35 7/8 in. long. Does she reject this shoelace?

Percent Error= (36-35.875)/36*100-use decimals in the formula

=0.125/36*100-find the absolute value

=0.003472*100-simplify the fraction


The percent error is 0.35% rounded to the nearest hundredth, the shoelace is not rejected.

ex. At a sporting goods factory, a quality control technician checking the weights of baseball bats measures a bat that should weigh 26oz. But weighs 26 1/4, if a bat is not within 0.6% of its specified weight, it is rejected. Should the bat be rejected?

student ex. At a model train factory, a quality control technician checks the weight of a passenger car that should weight 4lbs, but this car only weighs 3 1/2lbs. If a car is not within 0.5% of its specified weight, it is rejected, should this car be rejected?


Pages 251-252

Problems- 8-14 all

20, 23,28,29, and 31.

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