Alright my brother posed this question to me tonight. You have 7 coins (for this sake we will go with the "normal" coins, penny, nickel, dime and quarter) and we are trying to find the probability that a person has over a dollar in coins.(adsbygoogle = window.adsbygoogle || []).push({});

So basically I did it and just wanted to confirm my answer before telling him tomorrow morning.

You just do:

E(x)=((1*(1/4))+(5*(1/4))+(10*(1/4))+(25*(1/4)))

E(x)= 41/5 = 10.25

7*E(x)=71.75

Var(x)=E(x^2)-E(x)^2

Var(x)=187.75-105.0625

Var(x)=82.6875

7*Var(x)=578.8125

Now I believe that I can do normal Z score stuff to find probability with the continuity correction. So we are looking for P(Z≥100) so we'll flip it into 1-P(Z≤100). Then we will add the continuity correction to make it 1-P(Z>100.5) and calculate it from there. Am I right so far?

So I go:

(71.75-100.5)/(24.058)

Z≈-1.195

And thus, using R normal probability calculator we are looking at a final answer of .1160379. Did I do that all right? Thanks!

**Physics Forums - The Fusion of Science and Community**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# 7 coins - probability over a dollar

Loading...

Similar Threads - coins probability dollar | Date |
---|---|

I Coin toss with changing probability | Dec 17, 2016 |

I Probability of getting 3 heads or more in 20 coin flips | Jun 19, 2016 |

Toss coin probabilities (Bino vs Gauss approx) | May 24, 2015 |

What happens if you flip an infinite heads and tails coin? | Jan 6, 2015 |

Regarding probability bound of flip coins | Aug 7, 2013 |

**Physics Forums - The Fusion of Science and Community**