How do I solve this?

Question

A pay phone at a shopping mall charges $0.89 for the first five minutes and $0.12 for each extra minute ( or part of a minute).

a. Find the cost of a 15- minute call on this phone.

b. Find the cost of a 12 1/2- minute call on this phone.

Answer 1

A. For the first 5 minutes you calculate it as expected: 5*0.89 = 4.45. Then there are ten minutes left in the call charged at $0.12 per minute. Calculated by 0.12*10 = 1.2. Total cost of the 15 minute call is $5.65.

B. If by saying (or part of a minute) means that each extra minute is $0.12, but if there is a partial minute on the call, like 12 and a half minutes, then that half of a minute is still worth $0.12. Thus just like in part A, this first 5 minutes is worth $4.45. Then you have 8 minutes left to account for, we can round 7.5 up to 8 since that half of a minute is worth the same as a full minute. 8*0.12=0.96. Totaling the two values together, we get $5.41 as the cost for the 12.5 minute call.