Andy's average driving speed for a 4 hour trip was 45 mph. During the first 3 hours he drove 40mph. What was his average speed?

Question

Andy's average driving speed for a 4 hour trip was 45 mph.  During the first 3 hours he drove 40mph.  What was his average speed?

anonymous · Answer

This should be what was his average speed for the last hour of the trip.

anonymous · Answer

I know the direct answer to this question, but due to the honor code I can't really tell you. Remember that the average of anything is the sum of two numbers divided by how many numbers there are.

For example, (4+5)/2 = 4.5, or midway between 4 and 5.

In this example, you already know the average (45), 3 speeds, and you know that this happened over 4 intervals (how many numbers there are). You only need to figure out which number you're missing, and then solve for it.

anonymous · Answer

In the example you gave me, you already know the average*

anonymous · Answer

[(40+40+40+x)/4]=45   The last hour was 60mph.

anonymous · Answer

could you multiply the hours 4 and 3  with the difference from 45 to 40 to get the answer 60? or is that just coincidence? so, (Vf-Vi)(12)