A scuba diver dove from the surface of the ocean to an elevation of -79 9/10 feet at a rate of -18.8 feet per minute. After spending 12.75 minutes at that elevation, the diver ascended to an elevation of -28 9/10 feet. The total time for the dive so far was 19 1/8 minutes. What was the rate of change in the diver's elevation during the ascent? why descent time is 4.25

(-28.9-(-79.9))/(19.125-12.75-(79.9/18.8)) = 24.0 ft/min

To find the rate of change in the diver's elevation during the ascent, we need to determine the change in elevation and divide it by the time it took for the ascent.

First, let's calculate the change in elevation. The starting elevation during the ascent is -79 9/10 feet, and the final elevation is -28 9/10 feet. To find the change in elevation, we subtract the starting elevation from the final elevation:

Change in elevation = (-28 9/10) - (-79 9/10)
= -28 9/10 + 79 9/10 (since subtraction of negative is equivalent to addition)
= 51 feet

Now, we need to determine the time it took for the ascent. The total time for the dive so far was 19 1/8 minutes, and the diver spent 12.75 minutes at the depth of -79 9/10 feet during the descent. Therefore, the remaining time for the ascent can be calculated by subtracting the descent time from the total time:

Ascent time = Total time - Descent time
= 19 1/8 - 12.75
= 6 3/8
= 6.375 minutes

Finally, we can find the rate of change in the diver's elevation during the ascent by dividing the change in elevation by the ascent time:

Rate of change = Change in elevation / Ascent time
= 51 feet / 6.375 minutes
= 8 feet per minute

So, the rate of change in the diver's elevation during the ascent is 8 feet per minute.

Regarding your question about why the descent time is 4.25 minutes, I'm sorry but based on the information provided, the descent time is actually 12.75 minutes. The total dive time so far is 19 1/8 minutes, and the diver spent 12.75 minutes during the descent, leaving 6.375 minutes for the ascent.