<PRE><B>Question 392213</B>
19. A motorist traveled 115 km on an expressway at an average speed of 92 km/h
 and another 45 minutes on the other roads.
 If the average speed for his whole journey was 80 km/h, how far did he travel on the other road? 
:
Let d = distance  on the other roads
:
Change 45 min to .75 hrs
:
Write a time equation: time = dist/speed
:
express time + road time = total time
{{{115/92}}} + .75 = {{{((d+115))/80}}}
Find least common multiple
92: 2*2*23 
80: 2*2*2*2*5
LCM: 2*2*2*2*5*23 = 1840
:
Multiply equation by 1840, results:
20(115) + .75(1840) = 23(d+115)
:
2300 + 1380 = 23d + 2645
:
3680 - 2645 = 23d
:
1035 = 23d
d = {{{1035/23}}} 
d = 45 miles on other roads
:
:
Check solution by finding the times (total dist 115 + 45 = 160 mi)
115/92 = 1.25 hrs
other rd= .75 hrs
-------------------
160/80 = 2.00 hrs
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