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On Which Day Did They Start

The Chavez family starts out with 42 gallons of water and, after three days, has 24.6 gallons left. So, in the equation for the Chavez family, the y-intercept is 42. That is, y = 42 when x = 0.

When x = 0? Wait a minute. Is day zero the same as saying their first day? And isn't first usually represented by the number one? The distinction of when to begin counting is a tricky one. How would you handle this confusion with your students?


Let's see how Ms. England handles it with her students.