To find out how much the amount of water in the canteen should change every 10 minutes, we can start by calculating how much water a hiker should drink in that time period.
Since it is recommended that hikers drink 24 ounces of water in one hour (which is 60 minutes), we first calculate how much they would drink in 10 minutes:
\[ \text{Water per 10 minutes} = \frac{24 \text{ ounces}}{60 \text{ minutes}} \times 10 \text{ minutes} = \frac{24}{6} = 4 \text{ ounces} \]
Therefore, the amount of water in the canteen should decrease by 4 ounces every 10 minutes.
So the correct response is:
−4 ounces