Question

The cost of 16 notebooks at store J is $24. The notebooks at store J are all the same price. The cost of notebooks at store J are all the same price. The cost of store K is shown on the graph below.
Which store has the least expensive cost per notebook and how much?

Answer 1

Now, we know that at Store J, for 16 books is 24 bucks...hmmm how much is it for 10 books anyway?

$\bf \stackrel{Store~J}{\begin{array}{ccll} books&cost\\ \text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\ 16&24\\ 10&x \end{array}}\implies \cfrac{16}{10}=\cfrac{24}{x}\implies x=\cfrac{10\cdot 24}{16}\implies x=15$

so, that much at Store J.

now, look at the graph, notice the point when x = 10, y = 8, so at Store K, is 8 bucks for 10 books.

which is cheaper?  well, surely you'd know that.