Mathematics Brain Teasers.

[Guyver]

On 10/4/2018 at 2:00 AM, seanjo said:

I can only do it using -ve 0.01. Will be interesting to see the solution.

Ooops.  Guess I should have read the thread before answering.  I'm guessing that's not what he was looking for?

[Ozymandias]

On 05/10/2018 at 9:19 AM, danydandan said:

If my response is correct, I know it is, can you confirm please. I'll post a new teaser when you can confirm.

You are correct, Dan, so why not go ahead and post another.

[danydandan]

Ok....

A loaf of bread and a sweet cost one Euro and ten cents in total. The loaf of bread costs a Euro more than the sweet How much does the sweet cost?

[Ozymandias]

8 minutes ago, danydandan said:

Ok....

A loaf of bread and a sweet cost one Euro and ten cents in total. The loaf of bread costs a Euro more than the sweet How much does the sweet cost?

5 cent

[danydandan]

2 minutes ago, Ozymandias said:

5 cent

That was quick.

Correct!

Edited October 6, 2018 by danydandan

[Ozymandias]

A circle has a chord in it of radius length. What is the chord's perpendicular distance from the centre of the circle?

[danydandan]

21 minutes ago, Ozymandias said:

A circle has a chord in it of radius length. What is the chord's perpendicular distance from the centre of the circle?

Same length as the radius. Isn't it.

[Ozymandias]

2 hours ago, danydandan said:

Same length as the radius. Isn't it.

No. How can it be? The distance from the centre of the circle to its circumference is the radius and that would pass through the chord at right angles.

[danydandan]

45 minutes ago, Ozymandias said:

No. How can it be? The distance from the centre of the circle to its circumference is the radius and that would pass through the chord at right angles.

Read the question wrong.

(Root(3)/2)r

Edit: Root is square root.

 

Edited October 6, 2018 by danydandan

[Ozymandias]

1 hour ago, danydandan said:

Read the question wrong.

(Root(3)/2)r

Edit: Root is square root.

 

As Pat Short would say: 'That's riot'. There are no tricks in my questions! Your turn to set a teaser, Dan.

[danydandan]

Simple one now.

6/2(1+2)=x

What's x?

[Ozymandias]

19 hours ago, danydandan said:

Simple one now.

6/2(1+2)=x

What's x?

I was leaving this for others but nobody seems in the least bit  interested so I'll answer it.

Depending on how one applies the mathematical rules of precedence the answer is 9 or 1. As presented the answer is 1.

[Long explanation omitted here but note the 6/2 is not bracketed.]

Edited October 7, 2018 by Ozymandias

[danydandan]

17 minutes ago, Ozymandias said:

I was leaving this for others but nobody seems in the least bit  interested so I'll answer it.

Depending on how one applies the mathematical rules of precedence the answer is 9 or 1. As presented the answer is 1.

[Long explanation omitted here but note the 6/2 is not bracketed.]

Only one of them numbers are correct. Technically speaking, according to a mathematician friend if mine whom I agree with.
 In my opinion 9 is the correct answer simply because you should not calculate outside the parentheses first. Well you don't have to anyways.

So you end up with 3.3=9.

But I was looking for 1 and 9. Not one or the other. I can't think of another example of a simple equation that may have two answers

That was a snakie one. Your turn Ozy

 

Edited October 7, 2018 by danydandan

[Ozymandias]

2 hours ago, danydandan said:

Only one of them numbers are correct.

That is true, Dan. As presented, 1 is the correct answer, not 9.

2 hours ago, danydandan said:

Technically speaking, according to a mathematician friend if mine whom I agree with.
 In my opinion 9 is the correct answer simply because you should not calculate outside the parentheses first. Well you don't have to anyways.

Not so, Dan, the rules of precedence are black and white. You must always clear brackets first, i.e. perform bracketed operations first. 

6/2(1+2)=x     

6/2(3)=x         

6/6=x

1=x

Dividing the 6 by 2 before clearing the bracket is a breach of precedence.

My maths question is this: a spacecraft travelling in a straight line is one million kilometres from its destination. It is constrained to move in a very peculiar way. Each day it is allowed to move once by halving the remaining distance between it and its destination. How long before it reaches its destination?

[danydandan]

5 minutes ago, Ozymandias said:

That is true, Dan. As presented, 1 is the correct answer, not 9.

Not so, Dan, the rules of precedence are black and white. You must always clear brackets first, i.e. perform bracketed operations first. 

6/2(1+2)=x     

6/2(3)=x         

6/6=x

1=x

Dividing the 6 by 2 before clearing the bracket is a breach of precedence.

My maths question is this: a spacecraft travelling in a straight line is one million kilometres from its destination. It is constrained to move in a very peculiar way. Each day it is allowed to move once by halving the remaining distance between it and its destination. How long before it reaches its destination?

Here is my argument for nine, PEMDAS says to solve anything inside parentheses, then exponents, and then all multiplication and division from left to right in the order both operations appear (that's the key). That means that once you solve everything inside the parenthesis and simplify the exponents, you go from left to right no matter what. That means the problem should actually be solved like as below.

6/2(1+2).

6/2.(1+2).

6/2.3.

3.3.

9.

I think I heard that question before, I think the answer is it will never reach it's destination if it halves its distance each time.

[RAyMO]

13 minutes ago, Ozymandias said:

That is true, Dan. As presented, 1 is the correct answer, not 9.

Not so, Dan, the rules of precedence are black and white. You must always clear brackets first, i.e. perform bracketed operations first. 

6/2(1+2)=x     

6/2(3)=x         

6/6=x

1=x

Dividing the 6 by 2 before clearing the bracket is a breach of precedence.

My maths question is this: a spacecraft travelling in a straight line is one million kilometres from its destination. It is constrained to move in a very peculiar way. Each day it is allowed to move once by halving the remaining distance between it and its destination. How long before it reaches its destination?

Never get there. 

EtA damn Dan - I should have been quicker.

 

Edited October 7, 2018 by RAyMO

[danydandan]

10 minutes ago, RAyMO said:

Never get there. 

EtA damn Dan - I should have been quicker.

 

You seen it first, so if it's correct you can post a teaser.

[Ozymandias]

There is an argument over the answer between mathematicians and scientists/engineers. Mathematically (and that is what we are emphasising here) the answer is never - the destination can never be reached. However, the scientist/engineer will only ask how close is close enough, i.e. what level of accuracy is, for all practical purposes, acceptable.

[danydandan]

49 minutes ago, Ozymandias said:

There is an argument over the answer between mathematicians and scientists/engineers. Mathematically (and that is what we are emphasising here) the answer is never - the destination can never be reached. However, the scientist/engineer will only ask how close is close enough, i.e. what level of accuracy is, for all practical purposes, acceptable.

Interestingly if there is a limit to how small matter can be broken into, ie hadrons, quarks etcetca. We'd still never reach that destination if we had 100% accuracy. But in reality it's only as accurate as our resolution.

That was an interesting question, thanks.

Edited October 7, 2018 by danydandan

[danydandan]

In a petri dish, there is a fungus. Every day, the fungus doubles in size. If it takes 48 hours for the fungus to cover the entire petri dish, how long would it take for the fungus to cover half of the petri dish?

[Ozymandias]

4 hours ago, danydandan said:

In a petri dish, there is a fungus. Every day, the fungus doubles in size. If it takes 48 hours for the fungus to cover the entire petri dish, how long would it take for the fungus to cover half of the petri dish?

The answer depends on what you mean by 'size'. If size means area the answer is relatively simple. If, however, size means 'radius' of expansion then it is a little more complicated. But I'll let others have a go first.

[danydandan]

10 minutes ago, Ozymandias said:

The answer depends on what you mean by 'size'. If size means area the answer is relatively simple. If, however, size means 'radius' of expansion then it is a little more complicated. But I'll let others have a go first.

Area.

[danydandan]

10 hours ago, danydandan said:

In a petri dish, there is a fungus. Every hour, the fungus doubles in size. If it takes 48 hours for the fungus to cover the entire petri dish, how long would it take for the fungus to cover half of the petri dish?

Edit: Made a mistake Every hour, from Every Day.

[Ozymandias]

54 minutes ago, danydandan said:

Edit: Made a mistake Every hour, from Every Day.

As it stood the original was very simple. If the fungus doubles in area every day and covers the entire dish after 2 days (48 hours) then it covers half the dish in one day. But this amendment changes things.

I'll still wait to give others a go, otherwise it's only me and you, Dan. 

PS - the answer is still simple.

Edited October 8, 2018 by Ozymandias

[Ozymandias]

31 minutes ago, Ozymandias said:

... otherwise it's only me and you, Dan. 

Not implying that is a bad thing, you understand. I would quite enjoy trading teasers with you for the craic!