Charles is jogging while listening to his favorite album. He runs at 6 MPH when he's got music on and 4 MPH when he doesn't. His album is 40 minutes long. How many minutes will it take him to jog 6 miles? Think carefully first, then make a decision:
He runs at .1 miles per minute because 6 / 60 = .1. While the album is playing he can run 4 miles because 40 x .1 = 4. He has to run 2 miles without the album because 6 - 4 = 2. Without music he runs 1 / 15 miles per minute because 4 / 60 = 1 / 15. He will run the remaining 2 miles in 30 minutes because 2 / (1 / 15) = 30. It will take him 70 minutes in total because 40 + 30 = 70. So, the answer is 70.