Word Problem

[Austin787]

The following is the problem:

John drove part of 260km trip at 80 km/h and the rest at 100 km/h. Find the
distance he traveled at 80km/k if his total driving time was 2 hours and 30
minutes.

Any help will be appreciated

[Virgil]

In article <N6fi7.177508$g_3.31...@typhoon.austin.rr.com>,
"Austin787" <shutc...@austin.rr.com> wrote:

If he did the whole trip at 100 kph, it would take
(260k)/(100kph) = 2.6 hours.

But 2h 30 m is only 2.5 hours.

He can't make it in 2.5 hours even if he does the whole trip at the
faster speed.

Are you sure you presented the problem correctly?

[Austin787]

Thank you for your help. It was a trick question and I simply did not get
it. I was spending too much time on the formula and not seeing the big
picture. Thanks again.

"Virgil" <vmh...@home.com> wrote in message
news:vmhjr2-5527DB....@news1.denver1.co.home.com...

[Doug Magnoli]

Well, you can still do the problem according to the general method, it's just
that you'll probably find out that the distance he traveled at 80 km/h is
negative.

(260-x)/100 + x/80 = 2.5

2.6 - x/100 + x/80 = 2.5

x/80 - x/100 = -0.1

10x - 8x = -80

x = -40

So he drove -40 km at 80kph, which took -0.5 hr, and the other 300 km at 100
kph, which took 3 hours, and 3+(-0.5)=2.5. So there's your answer.

Now it's just a question of interpretation.

-Doug Magnoli