Answer:
[tex]\displaystyle \text{Function: }{y=20-3x,\\\text{Domain: }(-\infty, \infty)\text{ or }\mathbb{R}[/tex]
Step-by-step explanation:
If the boy initially had 20 cents, then the total number of cents he will have left after purchasing [tex]x[/tex] pencils is equal to the total cost of the pencils subtracted from 20. The total cost of [tex]x[/tex] pencils, in cents, is equal to [tex]3x[/tex], since each pencil is 3 cents.
Therefore, the total amount, in cents, that the boy has left, [tex]y[/tex], is equal to [tex]20-3x[/tex]:
[tex]\displaystyle \text{Equation: }\boxed{y=20-3x}[/tex]
The domain of this function is [tex](-\infty, \infty)[/tex] or all real numbers [tex]\mathbb{R}[/tex].
