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Posted (edited)

Quick one to add to this then:

 

You are given seven balls - all identical in colour and size. You are told one is slightly heavier, but not by enough that you are able to tell by hand.

 

You are also given a set of traditional balance scales (which will handle as many balls as you wish to balance on them) with strict instruction you are only able to use them twice.

 

How do you find the heavier ball?

Edited by korifugi
"a slightly heavier" gah!
Posted (edited)

I got all 3, but I will admit it took me a minute to catch the third one.

 

You are given seven balls - all identical in colour and size. You are told one is slightly heavier, but not by enough that you are able to tell by hand.

 

You are also given a set of traditional balance scales (which will handle as many balls as you wish to balance on them) with strict instruction you are only able to use them twice.

 

How do you find the heavier ball?

 

That one's easy :p (Highlight.. Also made this as an edit so people wouldn't get it in their plaintext emails)

Put one ball on the scale to find out how much it weighs. Keep track of this ball.

Put all the balls on the scale. If the weight on the scales is less than ((the first weight) x 7) the first ball is the heavier one. If it's more, remove balls one by one until the scale drops its weight more than the weight of first ball - the ball you just removed is the heavier one.

I'm an idiot that didn't clock on to 'traditional balance scales'. Correct answer below. Original wrong answer left up for the lulz

You put 3 balls on each side, with one left over. If the scales don't tip, the one left over is the heavy ball.

If the scales do tip, you do the same with that pile of 3 balls: one ball on each side, one left over. If the scale tips again, the tipped side is heavy. If the scales don't tip, the one left over is heavy.

Edited by Garacesh
Posted (edited)

I asked my daughter the Bat and ball one last night, lets just say after 10 minutes of wrong answers (one of which being £1.80) I am concerned with her schooling.

 

She's 13 BTW

Edited by GuyJD
Posted

Another one 'cause it's Friday.

 

There is a room with no windows that has three light bulbs in it - set away from the door, on the outside of the room are three lightswitches that you are told operate the three bulbs.

 

The door closes automatically, and cannot be held or propped open. Starting outside the room, you are told you may only go through the door once.

 

How do you work out which switch operates which bulb?

Posted
I asked my daughter the Bat and ball one last night, lets just say after 10 minutes of wrong answers (one of which being £1.80) I am concerned with her schooling.

 

She's 13 BTW

 

I once asked a 16 yr old who the first man on the moon was, they replied 'Gordon Ramsey'

 

Never had faith in the education system since.

Posted
Another one 'cause it's Friday.

 

There is a room with no windows that has three light bulbs in it - set away from the door, on the outside of the room are three lightswitches that you are told operate the three bulbs.

 

The door closes automatically, and cannot be held or propped open. Starting outside the room, you are told you may only go through the door once.

 

How do you work out which switch operates which bulb?

 

Ooh.. Ooh.. I got this one.

(Again, edit shenanigans so it's not emailed to people)

Flick the first switch. Wait five minutes. Turn the switch off. Turn the second switch on. Go inside.

The first switch controls the lightbulb that is now off, but hot.

The second switch controls the lightbulb that is switched on.

The third switch controls the lightbulb that is switched off and cold.

  • Thanks 1
Posted
Ooh.. Ooh.. I got this one.

(Again, edit shenanigans so it's not emailed to people)

Flick the first switch. Wait five minutes. Turn the switch off. Turn the second switch on. Go inside.

The first switch controls the lightbulb that is now off, but hot.

The second switch controls the lightbulb that is switched on.

The third switch controls the lightbulb that is switched off and cold.

 

Only works if you know all 3 are off at the start

Posted

So it turns out that if you do all the editing shenanigans and then your post is quoted, the answer is visible.....

 

My answer is therefore: check on Edugeek. Those guys can solve all your problems 😛

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