# Chapter 13 - Counting and Probability - Chapter Review - Review Exercises - Page 869: 24

$\frac{4}{9}.$

#### Work Step by Step

We know that $\text{probability}=\frac{\text{number of favourable outcomes}}{\text{number of all outcomes}}=\frac{n(E)}{n(S)}.$ Hence here because we have $4$ $\$1$bills,$n(E)=4$, in total we have$n(S)=4+3+2=9$bills, therefore$\text{probability}=\frac{4}{9}.\$

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