How many minutes will it take a runner to run 12 miles?

Question

A runner starts running a race as fact as he can, but gradually runs out of energy and slows down along the way.  He starts running at a pace of 6 minutes per mile.  After every 2 miles, he slows down by 1 minute per mile. Write a sequence to show how many minutes it will take him to run 12 miles.  

Answer 1

The first two miles each take six minutes.

The next two (3,4) miles each take five minutes.

The next two (5,6) take four.

Then three. (7,8)

Then two. (9,10)

Then one. (11,12)

 

6+6+5+5+4+...