Ralph buys a desk that regularly sells for $250 and a desk chair that regularly sells for $145. both items are on sale at 15% off, and a sales tax of x% is applied to both. Which expression does not represent the amount Ralph pays? Show your work.

A. (395) (0.0085x) + 395 (0.85)

B. (250+145) (1-0.15) (100+x/100)

C. (0.85+x/100) (250+145)

D. 335.75+3.3575x

C) (0.85 + x/100) (250+145) does not give the correct answer.

Explanation

A) works; adding the two costs together is 250+145=395. We multiply this by 0.85 because 100%-15%=85%=0.85. We also have x% tax, which is represented by x/100, added to 100% of the value, or 1.00. Altogether this gives us

395 (0.85) (1+x/100) = 395 (0.85 + (0.85x/100)) = 395 (0.85) + 395 (0.85x/100)

= 395 (0.85) + 395 (0.0085x)

B) works; we have 250+145 for the original price; we have 85% = 0.85 of the value; we also have 100% + x%, which is (100+x) / 100.

C) does not work; (0.85+x/100) (395) does not take into consideration that you are finding the tax after taking the 85%. This will simplify out to

0.85*395 + (x/100) (395) = 335.75 + 395x/100 = 335.75 + 3.95x, which is too much.

D) works; simplifying the expression from A, we have 395 (0.85) + 395 (0.0085x) = 335.75 + 3.3575x.