Answer:
(1)The percentage error is 6.897 % .
(2)The total cost of the wallet is $34.35 .
(3)The salesman's commission as a percent of his total monthly sales is 4% .
(4)The interest is $5400 .
Step-by-step explanation:
First part
Formula

Change in value = |Approx value - Exact value|
As given
Mark estimates that the distance from his house to his school is 15.5 mi. The actual distance is 14.5 mi.
Approx value = 15.5 mi
Exact value = 14.5 mi
Change in value = |15.5 - 14.5|
= 1
Put all the values in the formula


Percentage error = 6.897 % (Approx)
Thus the percentage error is 6.897 % .
Second part
The price of a wallet is $31.95 and the sales tax is 7.5%.
7.5% is written in the decimal form

= 0.075
Sales tax price = 0.075 × Price of the wallet
= 0.075 × $31.95
= $2.4 (Approx)
Total cost of the wallets = Cost of the wallet + Sales tax price
= $31.95 + $2.4
= $34.35
Therefore the total cost of the wallet is $34.35.
Third part
Formula

A sneaker store salesman had $4,125 in total monthly sales last month. He made $165 in commission from those sales.
Part value = $165
Total value = $4125
Put all the values in the formula


Percentage = 4%
Therefore the salesman's commission as a percent of his total monthly sales is 4% .
Fourth part
Formula

Principle = $12000
Rate = 15%
Time = 3 years
Put all the values in the formula


Simple interest = $5400
Therefore the interest is $5400 .