## 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

# comperr-like Impossible Math: The Elephant and The Mosquito

3 replies to this topic

### #1 unreality

unreality

Senior Member

• Members
• 6370 posts

Posted 11 July 2007 - 06:03 PM

Does the weight of an elephant equal the weight of the mosquito?

Let x be the weight of the elephant, y be the weight of the mosquito. Call the sum of the two weights 2v, then x+y=2v

From this equation we can obtain two more:

x - 2v = -y
and
x = -y + 2v

multiply:
x^2 - 2vx = y^2 - 2vy

x^2 - 2vx + v^2 = y^2 - 2vy + v^2
OR
(x-v)^2 = (y-v)^2

take square roots:

(x-v) = (y-v)

x = y

The elephant's weight equals the mosquitoes.

What is wrong here?
• 0

### #2 savagegamer90

savagegamer90

Junior Member

• Members
• 77 posts

Posted 11 July 2007 - 06:16 PM

when you take the square root you ignore an answer to the problem
• 0

### #3 mdsl

mdsl

Junior Member

• Members
• 51 posts

Posted 11 July 2007 - 06:37 PM

(x-v)^2 = (y-v)^2

take square roots:

(x-v) = (y-v)

Mathematically when you take the square root of both sides you need a plus or minus on at leat one side:

(x-v) = ±(y-v)

The minus route gives you x + y = 2v again. Obviously you should choose to use the minus out of the plus or minus because anyone would assume they cannot be the same mass, yet you get back to your original equation and realize you are just wasting your time like I just realized.
• 0

### #4 unreality

unreality

Senior Member

• Members
• 6370 posts

Posted 11 July 2007 - 09:06 PM

good job! that problem can get confusing.
• 0

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

0 members, 0 guests, 0 anonymous users