Question

you need to buy some pencils and an eraser. You can spend no more than $5. The eraser costs $1 and the pencils cost $0.25 each

Answer 1

Let E be the number of erasers and P the number of pencils, the cost for the erasers will be 1*E and the cost of the pencils will be 0.25*P.

Then, adding both, we get the total cost:

$C=E+0.25P$

If the total cost has to be 5 or less, we can define the inequality as:

$\begin{gathered} C\le5 \\ E+0.25P\le5 \end{gathered}$

We can solve this inequality as E in function of P or viceversa.

$\begin{gathered} E+0.25P\le5 \\ E\le5-0.25P \end{gathered}$$\begin{gathered} E+0.25P\le5 \\ 0.25P\le5-E \\ P\le\frac{5-E}{0.25} \\ P\le20-4E \end{gathered}$

Answer:

Being E the number of erasers and P the number of pencils, the inequality is E+0.25P<=5.

The inequality for E in function of P is E<=5-0.25P.

The inequality for P in function of E is P<=20-4E.