Carrie works 40 hours. she spends 15% of her time at the register, 30% of her time greeting customers, and the remainder of the time on maintenance. what percentage of carries time is spent on maintenance?

Call x the percentage of Carrie's time that is spent on maintenance.  We can write the following equation to solve for x: x+15+30=100, and subtracting 45 from both sides, we get x=55.  Therefore, 55% of Carrie's time is spent on maintenance.

Notice that how much time Carrie spends at work is extraneous information.  Remember, just because a problem gives you certain information doesn't mean you need to use the information to solve the problem!