Strange sum (riddle tread)
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08-09-2011, 10:36 PM
RE: Strange sum
Use a calculator...

Just kidding, it's 100 multiplied by the sum of the number before the 5 and the consecutive number after said number, plus 25.

For instance:
125*125= 100*12*13 + 25 = 15625

Hmm... technically using Zatamon's hint, we can actually obtain the square of every number.

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09-09-2011, 06:46 AM
 
RE: Strange sum
(08-09-2011 10:36 PM)robotworld Wrote:  Hmm... technically using Zatamon's hint, we can actually obtain the square of every number.

Only every number where the last digit is 5.

So, how would you use the same method to calculate the square of 455?

(in your head, sans calculator Tongue)

Another good one that I regularly asked my first year students when I was teaching in college:

Can you calculate the square of 999 in your head?
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09-09-2011, 01:37 PM
RE: Strange sum
In my head? Challenge accepted.

455*455
= 100*45*46 + 25
= 100*(45*45+45) +25
= 100*(100*4*5+25 +45) +25
= 100*(2070) +25
= 207025

999*999
= (1000-1)(1000-1)
= (1000000 -2000 +1)
= 998001

Here you go Big Grin

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09-09-2011, 02:05 PM
 
RE: Strange sum
Perfect.

My take on 999*999 = 1000*999 - 1000 + 1 = 998001

Isn't it fun?
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09-09-2011, 02:33 PM
RE: Strange sum
Riddles are fun! Here's one I thought of.

A heartless murderer, a soulless being,
Destroying everything you know or love.
He can be nimble, he can be slothful,
Destroying even the toughest substance,
Crumbling them into dust.
Who is he? And be quick.
For he shows no mercy to the slow.

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09-09-2011, 02:37 PM
 
RE: Strange sum
god?

Big Grin

Failing that -- time?
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09-09-2011, 02:53 PM (This post was last modified: 09-09-2011 02:59 PM by GirlyMan.)
RE: Strange sum
(09-09-2011 02:33 PM)robotworld Wrote:  Riddles are fun! Here's one I thought of.

A heartless murderer, a soulless being,
Destroying everything you know or love.
He can be nimble, he can be slothful,
Destroying even the toughest substance,
Crumbling them into dust.
Who is he? And be quick.
For he shows no mercy to the slow.

Booze.

Here's one that fucked with me back in the day until I was properly educated.

You're in the final round of Let's Make a Deal. There are 3 curtains. Behind 1 curtain is a car. Behind the other 2 is a goat and a pig. You pick a curtain. Monty Hall shows you a curtain with a pig behind it and gives you the option of keeping or changing your original curtain choice. What do you do? (Hint: one choice doubles your chance of winning the car.)

To me this is evidence that we don't intuitively appreciate probability. We are not instinctively Bayesian. Which of course is part of the reason why the house always wins. Wink

As it was in the beginning is now and ever shall be, world without end. Amen.
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Your shadow at morning striding behind you
Or your shadow at evening rising to meet you;
I will show you fear in a handful of dust.
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09-09-2011, 03:31 PM
RE: Strange sum
(09-09-2011 02:33 PM)robotworld Wrote:  Riddles are fun! Here's one I thought of.

A heartless murderer, a soulless being,
Destroying everything you know or love.
He can be nimble, he can be slothful,
Destroying even the toughest substance,
Crumbling them into dust.
Who is he? And be quick.
For he shows no mercy to the slow.

Time?

Behold the power of the force!
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10-09-2011, 01:16 AM
RE: Strange sum
Correct! It is indeed time! You people are good!

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10-09-2011, 06:38 AM
RE: Strange sum
(09-09-2011 02:53 PM)GirlyMan Wrote:  
(09-09-2011 02:33 PM)robotworld Wrote:  Riddles are fun! Here's one I thought of.

A heartless murderer, a soulless being,
Destroying everything you know or love.
He can be nimble, he can be slothful,
Destroying even the toughest substance,
Crumbling them into dust.
Who is he? And be quick.
For he shows no mercy to the slow.

Booze.

Here's one that fucked with me back in the day until I was properly educated.

You're in the final round of Let's Make a Deal. There are 3 curtains. Behind 1 curtain is a car. Behind the other 2 is a goat and a pig. You pick a curtain. Monty Hall shows you a curtain with a pig behind it and gives you the option of keeping or changing your original curtain choice. What do you do? (Hint: one choice doubles your chance of winning the car.)

To me this is evidence that we don't intuitively appreciate probability. We are not instinctively Bayesian. Which of course is part of the reason why the house always wins. Wink

We change our answer. When we first made the guess we only had a 33% chance of it being correct, however now we have a 50% chance of it being correct, so we change to the other curtain. I enjoyed statistics in both highschool and college, plus I like the movie 21!

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