In Arizona the group of 24 students visited the Grand Canyon. Some spent their time white-water rafting, while the rest went down into the canyon either by foot or by mule or both.
- The number who went by both mule and foot was twice the number who went solely by foot.
- The number who went only by mule was the same as the number who went white-water rafting.
- The number who went by foot was half the total number.

How many went white-water rafting?