# Heads occurs 15 times out of 20 - Is it a fair coin?

by phono
Tags: coin, fair, heads, occurs, times
 P: 3 1. The problem statement, all variables and given/known data I have to answer this question by using references to expectation and probability as well as any other relevant considerations. My textbook says that 96% of the time, the number of heads in 20 flips will be between 6 and 14 inclusive. How do I prove this?
 P: 1,874 Do you know about the standard deviation?
Emeritus
PF Gold
P: 9,421
 Quote by phono My textbook says that 96% of the time, the number of heads in 20 flips will be between 6 and 14 inclusive. How do I prove this?
Even if you answer this, it won't tell you the answer to the question in the thread title. Are you sure you gave us all the information?

Anyway, if you want to prove that 96% figure, you have to add up the probabilities for "exactly 6", "exactly 7" and so on. Do you know how to calculate those?

P: 86
Heads occurs 15 times out of 20 - Is it a fair coin?

 Heads occurs 15 times out of 20 - Is it a fair coin?
A fair coin is one which gives 50% heads and 50% tale when tossed for infinite number of times.

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