Four people are in the jungles of Maine at night. They have to cross a bridge as quickly as possible or the monster known as the Oversized People-eating Iguana (a.k.a. OPI) may gobble them up. They are impeded in their crossing because only two people can be on the bridge at once and they have only one flashlight. Two people must go over and one must come back with the flashlight to get the others. A person cannot cross the bridge without the flashlight or they are certain to fall and get eaten by the river sharks. The quick-witted accountant of the group estimates the OPI will reach them in 18 minutes. Your objective is to save all the members of the group—including the accountant.

The members of the group are sorted by how quickly they are able to cross. You have a 1,2,5 and 10-minute member. Here is an example of how to solve this problem: If the 1-minute and 5-minute person cross the bridge together, it takes them 5 minutes to cross. If the 1-minute person crosses back with the flashlight, that is another minute. Therefore the first trip takes 6minutes, and only one person is safely across.

1^st Crossing: 1-minute member and 5-minute member 5 minutes

1^st Trip back with flashlight is 1-minute member 1 minute

total 1^st trip: 6 minutes, only one member is safe, and you have less than 12 minutes left

What is the best combination of trips over and back to assure everyone crosses within 18 minutes?