Barry Garelick, via a kind email:
I had come to the point in the chapter on systems of linear equations in my algebra 1 class where the book presented mixture, rate and current, and number problems. To prep them for the onslaught, I included a word problem into one of the warm-up problems I had them do as I checked in their homework.
The problem was: “The length of a rectangle is 3 units more than the width. The perimeter is 58 units. Find the length and width.”
Students asked me “How do you do this problem?” as I came around to check their homework. I offered one hint: “You can solve it using the substitution method”.
“What does this problem have to do with the substitution method?” a boy named Lonnie asked.
I answered his question when I went over the warm-up questions. “If you solve the problem to find length and width you will have two equations in two unknowns which you can solve by substitution.”
Many students shouted at once.