Dennis wants to buy a card for his wife. dennis calculates the amount of the card as $ 4.50. the actual price of the card is $4. what is dennis's % error?

Okay, so this equation is a percent error, and how you solve those is doing:

First Subtract Approximate value from Exact value:
4.50 - 4 = 0.5 , so the error is 0.5

Now, show the error as a percent of the exact value ... so divide by the exact value and make it a percentage:

0.5/4 = 0.125 = 12.5%

Therefore the percent error would be: 12.5%

C. i believe it is (5×(-20))+(100×(0.7))