Answer :
Answer:
36 mph.
Step-by-step explanation:
Let x be the distance to the town hall.
Trip there:
speed (s) = distance / time
s = x / 1.5 so x = 1-5s
Trip back:
s - 12 = x / 2 so x = 2s - 24
AS they are both = to x:
1.5s = 2s - 24
0.5s = 24
s = 48.
Average speed on the way back = 48-12 = 36 mph.
Answer:
36 mph
Step-by-step explanation:
Let s represent the speed on the way back. Time is inversely proportional to speed, so the speed ratios are ...
(speed going)/(speed coming) = (s+12)/s = 2/1.5 = (time coming back)/(time going there)
1 +(12/s) = 4/3 . . . . . divide, simplify the ratio
12/s = 1/3 . . . . . . . subtract 1
s = 36 . . . . . . . . . multiply by 3s
Bill's average speed on the way back was 36 mph.
_____
I sometimes like to think of these problems in terms of "ratio units." We have the speed ratio:
(s+12)/s = 2/1.5 = 4/3
The difference between s+12 and s is 12 mph, and that corresponds to the difference 4-3 = 1 ratio unit. So 3 ratio units will be 36 mph, corresponding to the value of s. Bill's speed on the way back was 36 mph.
(48 mph)/(36 mph) = 4/3 . . . . check