436. The Crossing. Six relatives need to cross a river in a small boat that can only hold two people at a time. Mr. Webster, who was in charge of the crossing, had a falling out with his father-in-law and son. Unfortunately, I must also note that Mrs. Webster is not speaking to her mother and her daughter-in-law. The tension between them is so high that it would be unsafe to allow feuding parties to cross together or to remain on the same bank of the river. Additionally, to prevent further disputes, no man can be left with two women or two men with three women.

How can this respectable family cross to the opposite bank in the fewest number of trips? No tricks such as using a rope or swimming to another bank are allowed.
436. The puzzle can be solved in 9 crossings as follows:

1) Mr. and Mrs. Webster cross together;

2) Mrs. Webster returns;

3) the mother and daughter-in-law cross

4) Mr. Webster returns;

5) the father-in-law and son cross

6) the daughter-in-law returns;

7) Mr. Webster and the daughter-in-law cross;

8) Mr. Webster returns;

9) Mr. and Mrs. Webster cross together.