Chapter 13, Problem 33SGA

To determine

To find: The odds of each occurring event.

Answer to Problem 33SGA

The odds to get all three nickels is $\frac{1}{139}$ .

Explanation of Solution

Given:

The bag containing $7$ pennies, $4$ nickels, and $5$ dimes.

The given event: Three coins are drawn at random of them all are nickels.

Calculation:

The probability of getting three nickels is calculated as:

  $\begin{array}{c}P\left(E\right)=\frac{C\left(4,3\right)}{C\left(16,3\right)}\left[\begin{array}{l}C\left(4,3\right)\text{is the number of ways of selecting three nickels from the bag}\\ C\left(16,3\right)\text{is the number of ways of selecting three coins from the bag}\end{array}\right]\\ =\frac{\frac{4!}{\left(4-3\right)!3!}}{\frac{16!}{\left(16-3\right)!3!}}\\ =\frac{\frac{4!}{1!3!}}{\frac{16!}{13!3!}}\\ =\frac{4!\times 13!}{16!}\end{array}$

Further simplified as:

  $P\left(E\right)=\frac{1}{140}$ .

The probability of not getting three pennies is calculated as:

  $\begin{array}{c}P\left(E^{\prime }\right)=1-P\left(E\right)\left[P\left(E^{\prime }\right)\text{is probability of failure}\right]\\ =1-\frac{1}{140}\\ =\frac{139}{140}\end{array}$

We know that the odds of the successful outcome of an event is the ratio of the probability of its success to the probability of its failure.

  $\begin{array}{c}\text{Odds}=\frac{P\left(E\right)}{P\left(E^{\prime }\right)}\\ =\frac{\frac{1}{140}}{\frac{139}{140}}\\ =\frac{1}{139}\end{array}$

Therefore the odds to get all three nickels is $\frac{1}{139}$ .