<PRE><B>Question 539007</B>
Rashard drives 100 mi from Detroit to Lansing, and later drives 90 mi more from Lansing to Grand Rapids.
 The trip from Lansing to Grand Rapids takes him a half hour less than the drive from Detroit to Lansing.
 What is his driving average speed if it is the same on both parts of the trip?
:
Let t = time from Det to Lan
then
(t-.5) = time from Lan to G.R.
:
Write a speed equation, speed = dist/time
Speed was the same on both trips
:
{{{100/t}}} = {{{90/((t-.5))}}}
cross multiply
100(t-.5) = 90t
100t - 50 = 90t
100t - 90t = 50
10t = 50
t = 50/10
t = 5 hrs to Lansing
Find the speed
100/5 = 20 mph was his average speed
check the speed
90/4.5 = 20 mph</PRE>