Earl's appointment

[Brent@GMATPrepNow]

Earl leaving for an appointment in another state. If he travels at 60 miles per hour, he will arrive 1 hour early. If he travels at 40 miles per hour, he will arrive 2 hours late. At what speed, in miles per hour, must he travel to arrive on time?
(A) 50
(B) 460/9
(C) 360/7
(D) 310/6
(E) 160/3

[truplayer256]

Let x= total distance

x/60+1= Exact time
x/40-2= Exact time

Set both equations equal to each other in order to find the distance, x:

x/60+1=x/40-2
x=360

It takes 7 hours to get to the appointment. So, in order for Earl to be there exactly on time, he must go 360/7 miles per hour.
C?

[Brent@GMATPrepNow]

Nice solution. You made the distance the variable and set each expression equal to the requred time.
You can also make the time the variable and set each expression equal to the distance:
Let t be the length of time required to arrive on time
We get: 40(t+2) = 60(t-1)
We get t = 7 (7 hours)
If t=7, we can determine the total distance: 40 x (7+2) = 360 miles
Earl needs to travel 360 miles in 7 hours, so he must travel at 360/7 miles per hour