Question 959479: The Washington school PTA set up a phone tree in order to reach all of its members. Each person’s responsibility, after receiving a call, is to call two other assigned members until all members have been called. Assume that everyone is at home and answer the phone and that each phone call takes 30 seconds. If one of the 85 members, the PTA president, makes firs phone call and starts the clock. What is the least amount of time necessary to reach all 85 members of the group?
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! The Washington school PTA set up a phone tree in order to reach all of its members. Each person’s responsibility, after receiving a call, is to call two other assigned members until all members have been called. Assume that everyone is at home and answer the phone and that each phone call takes 30 seconds. If one of the 85 members, the PTA president, makes firs phone call and starts the clock. What is the least amount of time necessary to reach all 85 members of the group?
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Series:: 1 + 2 + 4 + 8 + ...
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a(1) = 1 ; r = 2
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Solve::
85 <= 1[(1-2^n)/(1-2)
85 <= 2^n-1
2^n >= 86
n >= 7
Ans:7*30 sec = 3.5 minutes
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Cheers,
Stan H.
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