Answer:
$ 7.7
Step-by-step explanation:
Given,
There are 18 $1 bills, ten $5 bills, eight $10 bills, three $20 bills, and one $100 bill,
Total number of bills = 18 + 10 + 8 + 3 + 1 = 40,
![\because \text{Probability}=\frac{\text{Favourable outcomes}}{\text{Total outcomes}}](https://tex.z-dn.net/?f=%5Cbecause%20%5Ctext%7BProbability%7D%3D%5Cfrac%7B%5Ctext%7BFavourable%20outcomes%7D%7D%7B%5Ctext%7BTotal%20outcomes%7D%7D)
Thus,
The probability of $ 1 = ![\frac{18}{40}](https://tex.z-dn.net/?f=%5Cfrac%7B18%7D%7B40%7D)
The probability of $ 5 = ![\frac{10}{40}](https://tex.z-dn.net/?f=%5Cfrac%7B10%7D%7B40%7D)
The probability of $ 10 = ![\frac{8}{40}](https://tex.z-dn.net/?f=%5Cfrac%7B8%7D%7B40%7D)
The probability of $ 20 = ![\frac{3}{40}](https://tex.z-dn.net/?f=%5Cfrac%7B3%7D%7B40%7D)
The probability of $ 100 = ![\frac{1}{40}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B40%7D)
If a bill is selected randomly,
The expected value of the bill
![=\frac{18}{40}\times 1+\frac{10}{40}\times 5+\frac{8}{40}\times 10+\frac{3}{40}\times 20+\frac{1}{40}\times 100](https://tex.z-dn.net/?f=%3D%5Cfrac%7B18%7D%7B40%7D%5Ctimes%201%2B%5Cfrac%7B10%7D%7B40%7D%5Ctimes%205%2B%5Cfrac%7B8%7D%7B40%7D%5Ctimes%2010%2B%5Cfrac%7B3%7D%7B40%7D%5Ctimes%2020%2B%5Cfrac%7B1%7D%7B40%7D%5Ctimes%20100)
![=\frac{18+50+80+60+100}{40}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B18%2B50%2B80%2B60%2B100%7D%7B40%7D)
![=\frac{308}{40}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B308%7D%7B40%7D)
= $ 7.7