Question

Question 10How many area codes of the form (XYZ)are possible if the digit 'X' and 'Y' can beany number 1 through 9 and the digit 'Z'can be any number 2 through 9?

Answer 1

`\begin{gathered} \#areacodes=x\cdot y\cdot z \\ \\ x\colon anynumber1through9 \\ x=9 \\ \\ y\colon anynumber1through9 \\ y=9 \\ \\ z\colon anynumber2through9 \\ z=8 \\ \\ \\ \#areacodes=x\cdot y\cdot z \\ \#areacodes=9\cdot9\cdot8 \\ \\ \#areacodes=648 \end{gathered}`