Math Riddle

[Mullit]

Hi, I saw this on a poster in the maths department at my college and thought Id post it here.

I will do the same thing to both sides of the equation in each step.

                             [B]A=B[/B]
multiply by B                [B]AB=B^2[/B]
take A^2                     [B]AB-A^2=B^2-A^2[/B]
Factorise                    [B]A(B-A)=(B-A)(B+A)[/B]
divide by (B-A)              [B]A=B+A[/B]
but A=B so                   [B]A=2A[/B]
                             [B]1=2[/B]

What Happened?

 

[AceHart]

> What Happened?

Not much. A simple divison by 0.

 

[phyrex1an]

If I remember right last time this was here there was a huge discussion regarding the errors of mathematic and general stupidness of humankind.
Lucky that ace was online this time too sort everything out before any weird ideas where born

 

[BlueSin]

Yeah I figured that out in my class in 8th when they showed us that.

 

[Mullit]

yeah, if A=B then B-A=0 or A-B=0. so then the dividing by B-A is dividing by 0 which cant actually be done so thats why it doesnt work.

I was hoping that this would take longer than 1 reply for someone to figure it out

 

[2-P]

Yep, next time you might want to check first if that AceHart thing is also online.

 

[SFilip]

A bit off topic, but here's another riddle some people might find interesting:
You have eleven different books and intend to sort them out on a bookshelf. How many possible combinations can you make?

 

[SilverHawk]

Assuming none are doubles, 39916800 (= 11P11).

 

[AceHart]

> Assuming none are doubles

Who cares? There's still 11 of them...

> 39916800 (= 11P11)

The number is correct. But I would read 11P11 as 11 to the 11th power, which would be slightly more...

 

[SFilip]

39916800 = 11! (11*10*9*8*7*6*5*4*3*2*1)

Anyone else has a riddle to post?

 

[idk_a_name]

Ive got one that I found...

A Ferrari is traveling at 30 miles per hour on a head-on collision course with a Maserati, which is being driven at a leisurely 20 miles per hour. When the two cars are exactly 50 miles apart, a very fast fly leaves the front fender of the Ferrari and travels towards the Maserati at 100 miles per hour. When it reaches the Maserati, it instantly reverses direction and flies back to the Ferrari and continues winging back and forth between the rapidly approaching cars. At the moment the two cars collide, what is the total distance the fly has covered?

ANSWER IN WHITE

At first glance it may seem that a horrendous calculation is necessary to solve this: the sum of an infinite series of numbers that get smaller and smaller as the cars approach each other. But if you focus on time rather than distance, a solution is easy. The cars are 50 miles apart and traveling towards each other at a combined speed of 50 miles per hour, so they will meet in one hour. In that hour, a fly that flies at 100 miles per hour will naturally travel 100 miles.

 

[Tonks]

Okay, here's one:
A truckdriver is going the wrong direction down a one-way street. A police officer sees the truck driver, yet he makes no attempt to stop him. Why doesn't the policeman do anything?

This one is more logic and reasoning than math.

 

[Duwenbasden]

Because he's driving in reverse...

 

[Tonks]

Because he's driving in reverse...

Did I say he was driving?

 

[Duwenbasden]

oh I so do hate you... :banghead: :banghead:

 

[KillerChi]

Did I say he was driving?

lol good one

 

[Amfidamant]

How about:


Will's got a Jug Full of Wine (8 Liters).
Now, he wants to give 4 Liters of Wine to hsi neighbour, but he has only 2 Jugs that are size of 3 and 5 liters.

How can he get 4 Liters?

This is pure logical riddle. I might made some spelling errors .

 

[Corleone]

Die Hard 2 ftw.
First you fill the 5 liter jug, pour 3 liters into the 3 liter one.
Empty the 3 liter one, and then pour the remaining 2 liters of the 5 liter one.
Then fill the 5 liter one, and pour 1 liter into the 3 liter one - which is still containing 2 liter - and voila! The 5 liter jug contains 4 liters.

 

[Mullit]

ok this ones not really a riddle its more of... my homework. Yes I know the answer im not just getting you guys to do my homework.

Find f'(x) of the following

f(x)=2ln(x^2-3)
f(x)=ln(x^3-3x)
f(x)=4ln(5-(2/x))

I will be impressed if i get lots of answers to this as I know a lot of the active members here arent over 16 and this is quite advanced.

 

[SilverHawk]

4x/(x^2-3)
(3x^2-3)/(x^3-3x)
(8/(x^2))/(5-(2/x)) <-- Don't feel like simplifying.

I'm not positive about these, but I think they're right. (Did them quickly.)

Ace:
11P11 means 11 permuations of 11. (Technically, the 11s should be subscripts, but i didn't know how to do that.)

Also, if there were doubles of the books, then there would be less, because multiple arrangements would look exactly the same, and are therefore not counted.