How's this for a math problem? A couple goes on a scuba-diving excursion on a boat filled with 18 other enthusiastic divers and a small crew. A crew member is responsible for ticking off on his clipboard divers who have returned from their dive.
One diver forgets his mask and remains on board. One tick. Another diver has trouble equalizing and returns early. Her partner comes along. Two more ticks makes three. The first diver asks if he can borrow a mask, but the crew member won't let him dive without a buddy, so the first and third divers go back in the water.
Here's the problem. The crew member has three ticks on his sheet, and only one diver remains in the boat. As the divers come back up, one by one, the ticks increase until 18 people are on the boat and 20 ticks are on the sheet.
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