Sam and Beth were standing at the edge of the swimming pool. "I can hold my breath for a whole minute," Sam told Beth. "Watch me. I'll stay underwater for one minute." He dived into the pool. Beth looked at her wristwatch. Sure enough, Sam stayed underwater for just about one minute.

"That's nothing," said Beth. "I can stay underwater for five minutes!"

"That's impossible!" scoffed Sam. "No one can hold their breath that long."

"I bet I can stay underwater for five minutes." Beth repeated. So Sam bet her. Beth won the bet. How did she do it?

• The answer