## Welcome to BrainDen.com - Brain Teasers Forum

 Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account. As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends. Of course, you can also enjoy our collection of amazing optical illusions and cool math games. If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top. If you have a website, we would appreciate a little link to BrainDen. Thanks and enjoy the Den :-)
Guest Message by DevFuse

# Speeding up

159 replies to this topic

### #51 Incognitum

Incognitum

Junior Member

• Members
• 51 posts

Posted 26 July 2007 - 05:23 PM

You know you only have 1 hour because it says "YOU TRAVELED HALF WAY" Half way of 60 is 30 and you are traveling at 30 PER HOUR, so if your total distance at that point is 30kh it MUST HAVE TAKEN 1 hour to do it. Now that your HOUR is used up, Even if you traveled at 4 billion miles an hour, you can not change the fact that your Hourly Rate of Travel "WAS" 30Km per hour.... s***, Now I'm confusing myself... My head hurts. . . . . . I need a drink.lol

I don't understand how you differentiate distance and time. How does having traveled half way in space mean unequivocally that your hour is used up? Why not say you've traveled halfway in space and halfway in time, so you have two hours total? Why does the distance dictate the time at all? The whole point of speed is the relation between distance and time, when you arbitrarily state that one supercedes the other the question of variable speeds becomes irrelevant.
• 0

### #52 Powerhouse

Powerhouse

Newbie

• Members
• 6 posts

Posted 26 July 2007 - 07:25 PM

For the people who believe this is possible I am sorry but you are wrong. You are looking at this from incorrect points of view. When you average speed you do not do it like averaging discrete numbers (i.e. 1,2,3... (whole numbers)). You divide the distance by the time it took to travel. Even if it took 0 seconds to travel the second half of the trip, your average speed would be (60 km)/(1 hr)= 60 km/hr. If you went 90 km/hr for the last 30 km it would take you 1/3 hr to reach town => the average would be 1.333 hrs (total time)/ 60 km (total distance) = 45 km/hr. To reach an average speed of 90 km/hr you would need to travel further.

Hope this helps explain.
• 0

### #53 Incognitum

Incognitum

Junior Member

• Members
• 51 posts

Posted 27 July 2007 - 04:27 PM

For the people who believe this is possible I am sorry but you are wrong. You are looking at this from incorrect points of view. When you average speed you do not do it like averaging discrete numbers (i.e. 1,2,3... (whole numbers)). You divide the distance by the time it took to travel. Even if it took 0 seconds to travel the second half of the trip, your average speed would be (60 km)/(1 hr)= 60 km/hr. If you went 90 km/hr for the last 30 km it would take you 1/3 hr to reach town => the average would be 1.333 hrs (total time)/ 60 km (total distance) = 45 km/hr. To reach an average speed of 90 km/hr you would need to travel further.

Hope this helps explain.

Thanks for the hot tip, however I feel my point of view is fine thanks. Perhaps next time try reading what we are saying before telling us we're wrong?

No one has been more swift then myself to correct those who think they've solved this puzzle by making an error in their arithmatic. However, your own post proposes a detour solution similar to the one we've been advocating.
• 0

### #54 Powerhouse

Powerhouse

Newbie

• Members
• 6 posts

Posted 01 August 2007 - 08:49 PM

When solving logic problems there are certain assumptions you are supposed to make. In this problem one of the assumptions is that you travel to town on a path and when you get half way there you dont take a detour while traveling faster to make up for the time spent traveling slower. The question is assuming you continue traveling only for another 30 km. "If I go halfway to town...how fast do I have to go for the rest of the way". So if you only travel another 30 km you cannot reach the desired average speed for the trip.

Picking apart the wording of questions is possible on most of these logic problems but it is not their intention.

Also my post wasnt directed towards people who understand the concept of averaging speed of a trip but for those who were trying to average 2 numbers because you traveled the same distance but not take into account the time.

So in conclusion yes you can travel more than 30 km and reach the average speed but the real solution is that it is impossible because the question implies that the first 30km is halfway.
• 0

### #55 Incognitum

Incognitum

Junior Member

• Members
• 51 posts

Posted 01 August 2007 - 09:47 PM

When solving logic problems there are certain assumptions you are supposed to make.

Foremost among them that there is a solution for those who are clever enough.

If 'it's impossible' is an acceptable answer for logic puzzles they are no longer any fun.

Q:
1. How many gray whales does it take to change a lightbulb?
2. How many cows would it take to create a particle accelerator?
3. What is the average IQ score for pairs of pants that have completed 7th grade?
4. How long would it take to fly to the moon inside your #2 pencil?
5. When your electric shaver rampages through the city killing thousands, how often does it need to be plugged in to recharge?

A:
1. It's impossible; all whales use energy efficient fluorescent lights that come with lifetime guarantees.
2. It's impossible; everyone known the key ingredient in particle accelerators is pork!
3. It's Impossible; even pairs of pants with PhDs cannot lift a pencil to take an IQ test.
4. It's impossible; all #2 pencils require air for their engines to fire.
5. It's impossible; what, you have a killer robot razor?

Now, was that any fun at all?
• 0

### #56 Powerhouse

Powerhouse

Newbie

• Members
• 6 posts

Posted 02 August 2007 - 02:02 PM

The difference between the speeding up question and the ones you posted is your first instinct in speeding up is figuring out what speed you have to travel then realising you cant do it. To me it was interesting because at first i was like thats easy..then theres the oh yeah I guess you cant do that. In your questions the assumption most people would or should make is that the situations you are talking about are not real and you are only looking for creative responses. To me speeding up is much more fun than the "think outside of the box" questions you posted.

But I guess to each his own.
• 0

### #57 fuzzywallaby

fuzzywallaby

Newbie

• Members
• 1 posts

Posted 06 August 2007 - 04:08 PM

Hmm... you know, this looks possible.

Lets see.....

For the first part of the journey, he travelled 30km at a speed of 30 kmh.

Time in the inertial frame of reference: 1 hour

unknown time = Time with respect to observer in inertial frame of reference
sqrt[1-(30kmh^2/c^2)]

unknown time: 59999999999.999699584484865522271 nanoseconds

Which gives him 0.00030041551513447773 nanoseconds to cover 30 km

=0.0000000000000050069252522412955 hours to cover 30 km

=5991701191578769.8403966508288831 kmh

He only needs to travel at 5991701191578769.8403966508288831 kmh to average 60kmh. =)
• 0

### #58 Powerhouse

Powerhouse

Newbie

• Members
• 6 posts

Posted 06 August 2007 - 04:28 PM

Haha.
• 0

### #59 Incognitum

Incognitum

Junior Member

• Members
• 51 posts

Posted 06 August 2007 - 09:03 PM

The difference between the speeding up question and the ones you posted is your first instinct in speeding up is figuring out what speed you have to travel then realising you cant do it. To me it was interesting because at first i was like thats easy..then theres the oh yeah I guess you cant do that. In your questions the assumption most people would or should make is that the situations you are talking about are not real and you are only looking for creative responses. To me speeding up is much more fun than the "think outside of the box" questions you posted.

But I guess to each his own.

I was actually attempting to interject a little levity into the conversation, but I guess I'm the only one who thought it was funny.

Seriously though, I do feel as though returning the answer 'it's impossible' is a defeatist way to approach a logic puzzle, but we may have to agree to disagree here.
• 0

### #60 rubarb1

rubarb1

Newbie

• Members
• 4 posts

Posted 09 August 2007 - 06:28 PM

There is nothing in the problem that says you have to go straight to town. You could do as the problem says, and travel 30km in one hour. Then take a detour and travel an additional hour at a rate of 90km per hour. Then you will have reached the town traveling a total of 120km in two hours, or an average of 60km per hour right?
• 0

#### 0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users