Hats and prisoners

Score Points: 5Solvers: 10

10 prisoners are given a chance of survival by the jailer. The jailer tells them that the next morning, he will have them stand in a queue (so that the last person can see the nine people in front, the second last people can see eight people in front of him, and so on), and then place either a red hat or a purple hat on each person's head. The person hence will be able to see the color of hat for people in front of him (but not his own hat). The jailer will then start from the last person, and ask each person "What is the color of hat on your head". The person can answer "red" or "purple". If the person's answer is correct, he will be released, else he will be killed. The jailer will then ask the same question to the second last person, and so on. The prisoners have the night to figure out the strategy so that maximum number of prisoners can survive (on a guaranteed basis). What is the maximum number of prisoners that one can guarantee will survive?

Correct Answer: 
9
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