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Another Maths Question For You


Wurzel
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My favourite similar question is the simple 3+4x5, which, appallingly, calculators on many modern smartphones etc get wrong, and many otherwise intelligent people argue over as a result.

 

How can any electronic device get that right ?

 

they all calculate intermediate results.

 

The written order defines the addition to be first.

 

The person typing it in needs to know BO(I)DMAS.

 

I bet you've had many a nite crowded round the coffee table with the Special Brew and ganga debating the phillosophy behind that..

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Only done O level myself, never heard of Bodmas (sounded like bidmas on radio but can't remember what he said second word was), so I just done it left to right as there were no brackets and got 1. They did say that this answer was understandable if you hadn't been taught the "advanced" way, so left to right was how majority would approach it.

 

Just thought it weird that what probably the majority of the population think the correct way to do a calculation like that is actually not the wrong way, which makes me wonder how easy it is for major mistakes to occur. Surely there should only be one right way taught.

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How can any electronic device get that right ?

 

they all calculate intermediate results.

 

The written order defines the addition to be first.

 

The person typing it in needs to know BO(I)DMAS.

 

A proper calculator made any more recently than about 1985 and not just free with a packet of corn flakes , uses 'true algebraic logic' and does not justdo the sums as it goes along. How they get away with putting such crappy ones on tablets and phones I don't know.

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Only done O level myself, never heard of Bodmas (sounded like bidmas on radio but can't remember what he said second word was), so I just done it left to right as there were no brackets and got 1. They did say that this answer was understandable if you hadn't been taught the "advanced" way, so left to right was how majority would approach it.

 

Just thought it weird that what probably the majority of the population think the correct way to do a calculation like that is actually not the wrong way, which makes me wonder how easy it is for major mistakes to occur. Surely there should only be one right way taught.

 

Sod the "advanced way", its more to do with a society that cant put its phone down and uses it for everything.

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A proper calculator made any more recently than about 1985 and not just free with a packet of corn flakes , uses 'true algebraic logic' and does not justdo the sums as it goes along. How they get away with putting such crappy ones on tablets and phones I don't know.

 

I just tried it on the TI calculator here in my desk, and it comes up with the right result, but only because it lets me put in more than one operator and I need to press "=" to get the result. Most devices calculate the result when you press the second operator nowadays.

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Only done O level myself, never heard of Bodmas (sounded like bidmas on radio but can't remember what he said second word was), so I just done it left to right as there were no brackets and got 1. They did say that this answer was understandable if you hadn't been taught the "advanced" way, so left to right was how majority would approach it.

 

Just thought it weird that what probably the majority of the population think the correct way to do a calculation like that is actually not the wrong way, which makes me wonder how easy it is for major mistakes to occur. Surely there should only be one right way taught.

 

Nothing to do with being taught any 'advanced way' ... just not being taught by an incompetent! BODMAS or its alternative forms is basic mathematical grammar in effect. Not being taught that is like not being taught to use a full stop in English.

 

There is only one right way taught.

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Sounds like some Yank perversion to me.

 

But you are right, BIDMAS seems to be equally valid.

 

It was BODMAS in my time too but the kids learned BIDMAS at school.

 

Not an Americanism as they apparently (Wiki) use PEDMAS (Parenthesis and Exponents...).

 

If you think about it Orders is to Exponents/Indices as Sharing is to Division.

 

Probably needed changing.

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Well while we're on brain teasers, here's a probability related one. It's quite well known so if you know it, feel free to share the answer but keep the rationale to yourself.

 

You're on a game show where they have placed a car behind one of three doors. Behind the other two doors are goats (don't ask). The host knows what is behind the doors.

 

You choose door 1, but the host doesn't open it, instead he opens door 3 to reveal a goat.

 

He then asks you if you want to stick with door 1 or change your mind and pick door 2.

 

So the question is...

 

Is it advantageous to change your original guess?

 

Why/why not?

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Nothing to do with being taught any 'advanced way' ... just not being taught by an incompetent! BODMAS or its alternative forms is basic mathematical grammar in effect. Not being taught that is like not being taught to use a full stop in English.

 

There is only one right way taught.

 

I left school with a Grade A O'Level Maths in 1978:blush:but don't recall anything other than left to right, brackets first. Would I have been taught "wrong" or just not progressed onto that level of maths (after all infants are taught correctly in basic addition etc but wouldn't have a clue about square roots etc) . If Bidmas is now taught in schools no wonder I was no use to my kids helping with their homework :uhoh:

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Well while we're on brain teasers, here's a probability related one. It's quite well known so if you know it, feel free to share the answer but keep the rationale to yourself.

 

You're on a game show where they have placed a car behind one of three doors. Behind the other two doors are goats (don't ask). The host knows what is behind the doors.

 

You choose door 1, but the host doesn't open it, instead he opens door 3 to reveal a goat.

 

He then asks you if you want to stick with door 1 or change your mind and pick door 2.

 

So the question is...

 

Is it advantageous to change your original guess?

 

Why/why not?

 

Stick with Door 1. Actually, I am just guessing.

Edited by alpine_saint
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Stick with Door 1. Actually, I am just guessing.

 

Is that cos the game show host is mugging you off Alps? I was thinking that, why would he open door 3! I said door 1 you homo! He clearly wants to keep the car for himself. He's trying to **** with my head or whatever.

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Well while we're on brain teasers, here's a probability related one. It's quite well known so if you know it, feel free to share the answer but keep the rationale to yourself.

 

You're on a game show where they have placed a car behind one of three doors. Behind the other two doors are goats (don't ask). The host knows what is behind the doors.

 

You choose door 1, but the host doesn't open it, instead he opens door 3 to reveal a goat.

 

He then asks you if you want to stick with door 1 or change your mind and pick door 2.

 

So the question is...

 

Is it advantageous to change your original guess?

 

Why/why not?

 

This is counter-intuitive. The best strategy is always to change your mind. Think of it this way. Choose a door that you don't want to be opened. The chance of it being a car is 1 in 3, so the chance of there being a car behind one of the other two doors is 2 in 3. The host will get rid of the spare goat for you leaving you with twice the chance of getting the car, providing you change your mind.

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It was called BODMAS in my day. Calculators vary in their priority sequencing. HP used to use reverse Polish which confused some people.

 

1 to the power 0 is 1, so the answer is 6-1+1, which is 1. (edit: that's a load of horlicks. I'd blame my IPad if I could. It's a good thing I showed my working). ;-)

 

It was an exercise for the reader. The answer is obviously 6, derbrain.

Edited by Whitey Grandad
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I've already got a car, I ain't got a goat. I'd change my guess to door 3.

 

Think again Bear man.

 

It's your car they're giving away. I know it's your car because the driver's seat is matted in thick ursine pelt and Tokyo-Saint is locked in the boot, hands tied behind his back, wearing nothing but a gimp mask and his charm.

 

Pretend you want to win the car back - you know, see Tokyos for one last time.

Edited by saintbletch
typo
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In the beginning you had a 33% chance of winning on the second attempt you have a 50% chance but only if you change otherwise you will stillbe at the 33%chance of your first attempt

 

66% if you change. The goat is removed for you, for free. The choice is first door (1 in 3) or second door (2 in 3) since if there is a car behind either of the two doors you will win it.

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66% if you change. The goat is removed for you, for free. The choice is first door (1 in 3) or second door (2 in 3) since if there is a car behind either of the two doors you will win it.

As there is only one car and you can only choose 1 door it reverts to 50% when the first goat is removed from the 3rd door. and you swap doors.

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Think again Bear man.

 

It's your car they're giving away. I know it's your car because the driver's seat is matted in thick ursine pelt and Tokyo-Saint is locked in the boot, hands tied behind his back, wearing nothing but a gimp mask and his charm.

 

Pretend you want to win the car back - you know, see Tokyos for one last time.

 

The way this is going looks like Tokyo is on his way to Manila after I've won the car Bearsy is he still useable?

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As there is only one car and you can only choose 1 door it reverts to 50% when the first goat is removed from the 3rd door. and you swap doors.

 

Are we talking a priori or a posteori? Sticking with the door is 33%. The alternative must be 66%

 

It's called the Monty Hall problem:

 

http://en.wikipedia.org/wiki/Monty_Hall_problem

Edited by Whitey Grandad
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The 'goat' problem is a standard statistics/probability brain teaser. I remember one of my Maths lecturers at uni giving us this in the 1970's, albeit expressed as a 'find the lady' gambling game, but the same principle.

 

The logic is .....

 

You should obviously change your mind if your first choice was wrong

 

When you made that choice there was a 1/3 chance you were right and a 2/3 chance you were wrong.

 

Therefore you were more likely to have been wrong and should change your choice.

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