Expressions from Stories

A shop sells pencils in boxes, and every box holds the same number of pencils. You do not know that number, so call it p. Sara buys 5 boxes and 2 loose pencils. The 5 boxes hold 5 times p pencils, which is 5p, and the loose pencils add 2 more: 5p + 2.

To turn a story into an expression, first find the unknown number and give it a letter. Then ask what happens to it. A thing that repeats, once for every box, is multiplied by the letter. A thing that comes once, like the loose pencils, is added on its own.

Why bother with a letter? One expression answers every version of the story. If a box holds 12 pencils, 5p + 2 gives 62. If it holds 20, it gives 102. The expression is the story's rule, written once.