Question 143301
Let's deal in minutes on this problem:

30 mph=(30*1/60 )mi/min=(1/2 )mi/min
Distance(d) equals Rate(r) times Time(t)or d=rt;  r=d/t and t=d/r
Also:
Average Rate=(Total Distance)/(Total Time)

Let t=time required to travel downhill
Total time, then, would be (4+t)
So, our equation to solve is:
1/2=2/(4+t)  multiply each side by 2(4+t)
(4+t)=4 subtract 4 from each side
t=0  THIS TELLS US THAT HE MUST TRAVEL THE SECOND MILE IN 0 TIME IN ORDER TO HAVE AN OVERALL AVERAGE OF 30 MPH

IF HE WANTS TO AVERAGE 30 MPH OR (1/2)MI/MIN OVER THE TWO MILES, THEN HIS TOTAL TIME HAS TO BE 4 MIN (2/(1/2)) BUT HE ALREADY USED UP HIS 4 MIN IN THE FIRST MILE!!!!! 


HOPE THIS HELPS---PTAYLOR