2007 QR problem

[ClosetNerd828]

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# 10 on the QR section of the 2007 DAT..

A person travels to work at an AVERAGE speed of 40mph, and returns home at 60mph. What, in mph, is the average speed for the entire trip?

The answer is 48mph.. I have no idea how this answer was found...

Any help would be greatly appreciated

 

[TraiDent]

Let's assume that the person's work is 100 miles away.
Time spent going to work @ 40mph means he spent 2.5 hours getting there
Time spent leaving work @ 60 mph means he spent 1.66 hours getting there.

So overall he spent 4.16 hours to travel a total distance of 200 miles (to work and back) which is 200/4.16 = 48.07 mph

 

[ClosetNerd828]

aaahhhh I see, the part I was missing was determining the # of hours spent driving. Got it. Thank you!

 

[ClosetNerd828]

Also while we are on the subjectof 2007 QRT... # 32 I cant figure out either..
y = (x+2)/ (x-3).. solve for x in terms of y..

this is basic algebra and for some reason I cant work it out..

the answer given is (3y+2)/(y-1)

 

[DAT Destroyer]

Also while we are on the subjectof 2007 QRT... # 32 I cant figure out either..
y = (x+2)/ (x-3).. solve for x in terms of y..

this is basic algebra and for some reason I cant work it out..

the answer given is (3y+2)/(y-1)

First cross multiply to get : xy-3y=x+2
Then put all terms that have x on one side: xy-x=2+3y then factor out x to get: x(y-1)=2+3y then divide: x =(2+3y)/(y-1)

 

[ClosetNerd828]

uugghhh I see... stinking algebra.. thank you

 

[DAT Destroyer]

uugghhh I see... stinking algebra.. thank you

🙂