Riddle Keeper

An expedition of 20 scientists crashes on an island and are captured by the natives. They will give the group one chance to escape.

The chief explains the test: “I will line you up single-file, all of you facing the same direction. We will then place on each of your heads a crown made with either red or blue flowers. It will be completely random. You will be able to see the crowns of everyone in front of you but none of the ones behind you. Starting from the back of the line each of you must guess the color of his or her own crown. All you may say is ‘red’ or ‘blue,’ nothing else. Everyone will be able hear everyone else’s answer. If you guess wrong, you will be killed by a poison dart. If you guess correctly, you will be freed.”

The chief then gives the group time to discuss a strategy to try and save as many of them as possible. One scientist says “We’ll just all call out the color of the crown in front of us. We’ll save at least 50% that way.” His colleague says “No, I have plan that will save at least 19 and maybe all of us!”

What is the plan?

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