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Video: Solving Word Problems Involving Rate of Change

Kathryn Kingham

The table shows the value of a company’s stock over a 5-day period. Determine the rate of change (dollars per day) between Day 1 and Day 3.

02:13

Video Transcript

The table shows the value of a company’s stock over a five-day period Determine the rate of change, dollars per day, between day one and day three. This question wants to know the rate of change between day one and day three, so we’ll start by highlighting day one and day three. But what does the rate of change mean? For this question, we’re looking at dollars per day, which means we need to look at the change in dollars over the change in days. What was the change from 40 dollars and 23 cents to 49 dollars and 87 cents?

To figure this out, we’ll subtract 40 dollars and 23 cents from 49 dollars and 87 cents. And how many days changed? We went from day one to day three to figure out how many days we’ll subtract three minus one. 49 dollars and 87 cents minus 40 dollars and 23 cents equals nine dollars and 64 cents. Three minus one is two.

Now we have nine dollars and 64 cents in two days. That’s a rate. But is this the correct rate that we’re looking for? It’s not, because our instructions are asking for dollars per day. And what we’re showing now is dollars per two days. To find dollars per day, we’ll need to divide the numerator and the denominator by two. Nine dollars and 64 cents divided by two equals four dollars and 82 cents. So our rate of change was four dollars and 82 cents per day.