On a foggy night, a passenger car and a truck meet on a bridge that is so narrow that the two vehicles can neither neither pass nor turn. The car has proceeded twice as far onto the bridge as the truck, but the truck has required twice as much time as the car to reach this point. Each vehicle has only half its forward speed when in reverse. Which of the two vehicles should back up to allow both of them to cross the bridge in the minimum time?
2009-07-31 01:14:32
Message 2
Join Date: July 2008
posts: 345
This could be done a bit faster I guess.....
Let the time taken by car to travel the distance mentioned be 2 hrs.
Given that the truck has traveled half this distance in 4 hrs.
So, now if the car backs up, it will take 4 hrs to go back and the same distance will be covered by the truck in 8 hrs which means the car will go back first and has to wait for 4 more hrs for the truck to clear the bridge. After this the car will clear the bridge in 3 hrs. So time taken here = 8 + 3 = 11 hrs
I think we can quickly eliminate the case of truck back up here
If the truck backs up..forget the time taken for this.....in order to clear the entire bridge the truck will alone take 12 hrs which is more than the time taken in the previous case.
Hence, the car must back up.
2009-08-03 21:13:21
Message 3
Join Date: July 2008
posts: 345
hello sir
my name is raj
i have a doubt in time and distance topic
the problem is
"hero and hercules start simultaneously from P towards the same destination Q.when the distance between hero and hercules was 30 KM champ starts towards Q .the distance travelled by champ to overtake hercules is twice the distance travelled to overtake hero.the ratio of speeds of hercules and hero is 3:2.
1. what is the ratio of the speed of champ to hero?
a.4:1
b.3:1
c.2:1
d.none of these
2. what is the distance between hero and hercules when champ was equidistant from hero and hercules?
a.45KM
b.48KM
c.51.42KM
d.54.57KM
2009-08-08 02:40:46
Message 4
Join Date: July 2008
posts: 345
These two can be answered a bit fast if you can understand the following reasoning....
It is evident that by the time Champ started Hero has covered 60 km and Hercules has covered 90 km.
From the given question we can conclude that if d km is the distance covered by Champ to meet Hero, from the point where he met Hero he should travel another d km to meet Hercules.
Now since Champ meets Hero after traveling a distance of d km, it is implied that Champ traveled 60 km more than Hero. Now since he traveled another d km to meet Hercules, it is implied that by the time Champ meets Hercules, Hero is 60 km behind them.
So by the time Champ meets Hercules, the distance between Hero and Hercules is 60 km. Since the speed ratio of Hero and Hercules is 3 : 2, by the time Champ met Hercules, Hero covered 120 km out of which 60 km was covered earlier.
Hence, by the time Hero covers 60 km, Champ covered 180 km and hence the speed ratio of Champ and Hero is 3 : 1
So folks, you can avoid equations if you can put this reasoning into the question and I am sure this will be the quick way to solve this.
Let us look at the second question now
From the first question we have the speed ratio of Hercules, Hero and Champ as 3 : 2 : 6
Since, by the time Champ started Hero is 60 km ahead, Champ has to travel 60 km more than Hero in order to meet him. From their speeds ratio we can conclude that if Champ travels 90 km, in the same time Hero covers 30 km and thus Champ meets Hero after traveling 90 km. In the same time Hercules covers 45 kms.
Thus by the time Champ meets Hero, Hercules is 45 km ahead of them.
Let us suppose that 3x km be the distance that Hercules has to travel from here so that Champ is exactly in between Hero and Hercules.
If Hercules covers 3x km, in the same time Hero covers 2xkm and Champ covers 6x km.
So now the distance between Hero and Champ is 4x km and the distance between Champ and Hercules is (45 - 3x) km
Given that 4x = 45 - 3x
i.e x = 45/7 = 6.42 km.
The distance between Hero and Hercules is 45 + x = 51.42 km
If you buy bags and purses of the latest new designs from the louis vuitton outlet now, you can enjoy special discounts. What else are you waiting for?
Owning louis vuitton bags of their own has been the dreams of many fad-seeking people for a quite long time.Have you ever dreamed of being as charming as Madonna? Have you ever thought of becoming an envy of all your friends? If so, come to louis vuitton outlet.
louis vuitton outlet is really so well-liked and also treasured during the human beings to be a number of high-end, they may realize that the bring up to date might impact their very own laurels signature in the fashion world as well as talk about in your predisposition in their enthusiasts.
2011-10-17 07:56:38
Message 8
factoryoutlet
Join Date: July 2008
posts: 345
This brown handbag called Flagship Signature Brown Handbag has been the best seller in the coach factory outlet for almost three weeks.There are different kinds of crossbody bags within marketplace nowadays. Even so it is not possible to beat the timeless design jointly with traditional elegance of the Bags at the coach factory outlet online.
coach factory outlet has a big heart and a healthy appetite, and a wicked swing with a chainsaw. After a knee injury ended his career as a defensive lineman in college, Coach salvaged his Physical Education degree(barely)and landed a job teaching health at the local high school in his hometown of Savannah.
Though handbags are basically an accessory item of girls, there are many modern handbags and wallets for males too as it has become the ultimate fashion accessory at coach factory outlet.coach factory online is the prior choice on the market today, because you can change the value of the innovative design of the fashion and high quality hides are popular, because of other accessories, best option.
2012-04-03 11:39:22
Message 9
store
Join Date: July 2008
posts: 345
Here you can find the latest products in different kinds of
,
introduced in 2004. This mounting mechanism-a decidedly unglamorous
element of the rifle scope,to most people-provides more reliable
mounting, and rapid switch of the scope from one rifle to another.The
high lead content in
makes them heavier than standard glass crystals and also increases the
index of refraction, which in turn makes them sparkly like diamonds when
they come into contact with light.
,
the normal progress of work, probably even this year, 45 months later
to the Chinese shop. However, in Wuhan, a high-end shopping malls and
the efforts of the international brand, grab one week before the Spring
Festival opened up. Avoiding the Major Pitfalls of Choosing the Wrong
Baby Pushchair It is pretty incredible how much of a significant
difference Baby pushchairs can have, of course you have to consider
certain factors. This is simple to comprehend and natural, and it is not
something that only affects you. It is not hard to find out more about
this, and you can potentially save yourself some hassles by doing so.
When you are pleased that your investigation is thorough, then that is
the time to evaluate the possibilities. The important thing is you need
to know the following about Baby pushchairs so you can make an informed
decision.Did you ever try wartrol Over the years you are going to have
to buy a lot of stuff to fulfill your baby??s needs. The most common
items are the bed, pushchair, toys. Bottles and pacifiers, and car
seat.Paypal
combined with Chinese style, the international trend of the subversive
elements in bold, the idea of ?weaving in elements in the interpretation
of low-carbon fashion casual.The
Join Date: 
Crash Course for IIT JEE 2010, AIEEE 2010 & BITSAT 2010 - Online + Postal Correspondence Courses
Similar Topics