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In a long hallway there are 100 lightbulbs in a row with draw-strings for a switch. All lights are initially off.
The first person goes through and pulls every draw-string (thus turning all the lights on). The second person goes through and pulls every second string, i.e. #2, #4, #6, etc...(thus turning some off)
The third person goes through and pulls on every third cord, and so on ...
The last, 100th person, goes through and pulls on the 100th string.
Which lightbulbs will stay on?
The first person turns them all on.
Since the second person through 100th person don't touch the first one, it will stay on.
The second person turns off #2, no one else touches it.
The third person turns off #3, no one else touches it.
The fourth person turns on #4, no one else touches it.
The fifth person turns off #5, no one else touches it.
Every person from 51-100 changes only their numbered bulb.
I could figure more, but this may be a trick question, too.
More: All prime numbered bulbs will be off. Person 1 turns them on, person (PN) turns it off, high numbers don't touch it.
Quote:
A coin was sold for $10 plus half of its price. What was the price of the coin?
$20.
More: The math isn't at all tough. Let P = half the price, 2P = price. Coin sold for $10+P = 2P. Subtract P from each side: $10 = P, 2P = $20.
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Using only addition (the "+" sign) express number 28 with five 2's.
22+2+2+2=28
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Using only addition (the "+" sign) express number 1000 with eight 8's.
888+88+8+8+8=1000
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Using any arithmetical symbols express number 100 with five 1's.
111-11=100
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Using any arithmetical symbols express number 100 with five 5's. (This problem has three different solutions.)
(5*5*5)-(5*5)=100
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A driver looked at the odometer and noticed that it showed a symmetric number, 15951. Wow, he thought, that doesn't happen often!
He continued on with a constant speed, and exactly in two hours glanced at the odometer again. To his amazement it showed a symmetric number again.
What was the speed of the car?
Unless he has rocket power, the first (and last) numbers must be 1: 1***1
The second (and fourth) numbers can't be more than 6, and can't be 5 or less: 16*61
Possibilities: 16061, 16161, 16261, 16361, 16461...
Which are 110, 210, 310... miles in two hours
210 (105 mph) is possible, but 110 (55 mph) is the likely answer.
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Posted 03/31/2012 9:50 pm
