Question

Abi had 20 cents. She bought x pencils for 3 cents each. If y equals the number of cents left, write an equation that shows the dependence of y on x . What is the domain of the function?

Answer 1

An equation that shows the dependence of $y$ on $x$ is $y=20-3x$ and the domain of the function is $x=[0,6], x \in N$.

Total number of cents $= 20$.

She bought $x$ pencils for $3$ cents each.

Let $y$ equals the number of cents left.

So, $3x+y=20$.

$y=20-3x$

Here $y$ must be positive

So, $20-3x>0$

$20>3x$

$\frac{20}{3}>x$

Domain of a function is the set of values for which the function is defined.

So, $x$ can get values from $0$ to $6$.

Therefore, the domain is:  

$x=[0,6], x \in N$.

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