How many pens go missing per day

Question

Ms. Hunter bought a box of 75 pens for her students to use in class. After 4 days, she had 63 pens left and after 15 days she only had 30 left. Assume her students are using them at a constant rate.

Answer 1

If you think about this problem in terms of a plot of the number of pens versus days, you might see how to find the answer.