All Answers

theiswe:
You can ask either of the twins the following question: "Which way would the other twin tell me to go?" and then you go the opposite direction!

Lets say Left is the correct way, and right is the wrong way.
If you ask the truthful twin (A) which way the other twin (B) would tell you to go, twin A will tell you that twin B would say "Right".
If you ask the lying twin (B) which way the other twin (B) would tell you to go, twin B will tell you that twin A would say "Right".
Therefore you should go the opposite way of what either of the twin replies to your question

Correction: If you ask the lying twin (B) which way the other twin (A) would tell you to go, twin B will tell you that twin A would say "Right".

Could not edit my previous post,thus a new post to correct myself.

GuestJan 29, 2014

+2354

4+6/3

reinout-gJan 29, 2014

+2354

[center]test[/center]

4+6x^2 = 5

reinout-gJan 29, 2014

+2354

reinout-g:
reinout-g:
[input](20*6^4*4+3)/(5+3)[/input]

[input]x^2+x = 3x+x^3/46[/input]

[input]x^2+y = 3xy/y^2[/input]

reinout-gJan 29, 2014

+2354

reinout-g:
[input](20*6^4*4+3)/(5+3)[/input]

[input]x^2+x = 3x+x^3/46[/input]

reinout-gJan 29, 2014

+2354

erawls:
50% of 90

90 * 50/100 = 45

reinout-gJan 29, 2014

+2354

Soup:
In a certain isosceles right triangle, the altitude to the hypotenuse is 4sqrt{2}. What is the area of the triangle?
I suck at geometry... please help

Here's the hint I'll give you

triangle.png

we know the left up corner and the right down corner are 45 degrees because the two sides adjecent to the right angle are of equal length.

We know the altitude always makes a 90 degree angle with the hypotunes,

From there we know the other two 45 degrees,

now with the use of properties of isosceles right angled triangles and pythagoras theorem you should be able to solve this.

If you're still in trouble or dont know pythagoras theorem, let me know

reinout-gJan 29, 2014

+2354

Guest:
what is the persents of whole numbers

I suggest you look at these two pages,
they'll give a more accurate definition than I can give you.

http://www.mathsisfun.com/definitions/percent.html

http://www.mathsisfun.com/percentage.html

reinout-gJan 29, 2014

+11

You can ask either of the twins the following question: "Which way would the other twin tell me to go?" and then you go the opposite direction!

Lets say Left is the correct way, and right is the wrong way.
If you ask the truthful twin (A) which way the other twin (B) would tell you to go, twin A will tell you that twin B would say "Right".
If you ask the lying twin (B) which way the other twin (B) would tell you to go, twin B will tell you that twin A would say "Right".
Therefore you should go the opposite way of what either of the twin replies to your question

GuestJan 29, 2014

+2354

Werter_380:
f(f(x)) = 13 - 2(f(x))
Decide f(f(x))

Sorry, but without a single solution such as for example f(0) = 1 this cannot be written in another way.

Perhaps I like Serena or Melody know something different then me about this, but it might take a while before they look at this.

reinout-gJan 29, 2014

+2354

Guest:
x to the fifth power-2x to the fourth power+10x to the 3rd power - 10x squared+20x+8

x ⁵-2x ⁴+10x ³-10x ²+20x+8

This is already written in the simplest form you can write it in

If you meant to have it solved, you first have to have it be equal to something else like for example x² - 3 = 6

reinout-gJan 29, 2014

+2354

The surface of a circle is given by r ²pi where r is the radius (1/2 * diameter)

Just like in the case of a cube where you need to multiply the ground surface (which in the case of the cube is lenght * width) with the height.

Hence the formula is given by r ² * pi * height where r ² * pi is the ground surface

reinout-gJan 29, 2014

+2354

kayleigh:
:lol: how do you find the volume of a cilinder

reinout-gJan 29, 2014

+2354

Vraces:
Ok, I got most of that.
But, I'm still wondering why is 0.75 irrelevant? And how do you [^] a number on this page?

I see melody beat me too it, yet I can help you with this question,

First look at the following equation;

1-0.25 ^(1/60) =NOT= 0.75 ^(1/60)

why are they not equal?

look at this equation (which makes it a little easier to explain)

1-0.25 ^(1/2) =NOT= 0.75 ^(1/2)
(1-0.25 ^(1/2)) ² = NOT= 0.75 ^(1/2)*2
1-2*0.25 ^(1/2)+0.25 ^(1/2)*2 = NOT = 0.75 ^(1/2)*2
1-2*0.25 ^(1/2)+0.25= NOT = 0.75
1-2*sqrt(0.25)+0.25 = NOT = 0.75

The same things happens when I take both sides of 1-0.25 ^(1/60) =NOT= 0.75 ^(1/60) to the power of 60

To give you an explanation 0.25 ^(1/60) gives what percentage is left each year if there is 25% left after 60 years.
1-0.25 ^(1/60) = what percentage the radioactivity reduces by each year.
0.75 ^(1/60) gives what percentage is left each year if there is 75% left after 60 years.

edit: you can click the button sup to make 'superscript' which is similar to ^, the other button sub gives subscript which you can use if you for example want to do this X _{the amount of chips} + Y _{the quality of TV} = Z _{damage to couch}

reinout-gJan 29, 2014

+2354

Vraces:
I need to understand why for example
[A radioactive kalashnikov gets less radioactive every year. After 60 years only 25% of the radio-activeness remains. What is the yearly reducing of radio-activeness in percent?]

I'm wondering. Since(Based on my assumption) 0.75^(1/60) should be in english: 75% of of the radioactiveness in one year. Since 75% was removed during 60 years shouldn't 0.75^(1/60) be the answer?[1 - 0.25^(1/60) = 0.75^(1/60)? ] And also. Why should it be ^(1/60) and not the percentage divided by 60?What does ^(1/60) actually mean? What happens when it calculates? I'm aware it multiples itself the times stated. For example: 3^3 = 27 ; 3^3(1/3) = 9 I must understand these things. It's good to know how to solve something, but if you don't know the meaning of it you can't solve another thing. I'm going to guess only Melody could explain this, but others are also welcome. IF you actually know the significance. Do not guess while trying to explain as it would only confuse me. And by the way, I may have confused you a little bit with what I'm trying to say. Good luck and thanks.

Dear Vraces,

I understand your confusion, and since Melody has just called it a day, I will do my best to give you the most clear and understandable explanation I can give you.

First let me calculate the following things for you;

a) 0.75/60 = 0.0125

b) 0.25^(1/60) = 0.9771599684342459

Suppose we have 100 kilograms of radioactive material, then we know that after 60 years only 25 kilograms will be left.

the first percentage is what we use if something reduces with 0.0125 of the original amount each year.

So in the case of the radioactive material this would mean that after 1 year the radioactive material would be

100-100*0.0125 = 98.75

after year 2 it would be

98.75 - 100*0.0125 = 97.5

which is the same as

100 - 100*0.0125 - 100*0.0125 = 97.5

which is the same as

100 - 2 * 100*0.0125 = 97.5

so after the 60 years it would be

100 - 60*100*0.0125 = 25 kg

As you can see, the radioactive material would then reduce with an amount of 1.25 kg each year

However, this is not what actually happens, because what actually happens is that the radioactive material reduces with the same percentage each year

If we calculate the percentage that is reduced each year in the above case we get;
1.25/100 * 100% = 1.25%
1.25/98.75 * 100% = 1.27%
1.25/97.5 * 100% = 1.28%
etc.

We want to reduce the material with a percentage per year,
Now let me give an example which will make you understand,

Suppose the radioactive material reduces with 2% each year
Then after 1 year we know we have 100kg * (1-0.02) = 100kg * 0.98 = 98kg
After 2 years we know we have 98kg*(1-0.02) = 98kg*0.98 = 96.04kg
or we can calculate it as 100kg * (1-0.02) ² = 96.04kg
After 5 years we know we have 100kg * (1-0.02) ⁵ = 90.39kg

(remember 2% reduction means 98% remains, which is why it is (1-0.02)=0.98)

Now lets turn the question around,
Suppose we do not know by how many percent the radioactive material reduces per year but we do know that after 5 years there is only 90.39 kg of 100kg left.

Then we know 100kg * (the percentage that is left per year) ⁵ = 90.39
We can rewrite this to (the percentage that is left per year) ⁵ = 90.39/100
and finally (the percentage per year) = (90.39/100) ^(1/5) = 0.98 = 1-0.02
So 1-(90.39/100) ^(1/5) gives us the percentage the radioactive material reduces by each year!

Now to get back to your question,

we know that in 60 years only 25% will be left, hence to calculate what percentage will be left every year we have (0.25) ^(1/60) = 0.977

Suppose again we have 100kg, in year 1 the amount that will be left can be calculated by
100*0.977 = 97.7 (so it reduced by 2.3 kg)

in year 2 the amount that will be left can be calculated by

100*(0.997) ² = 95.5 (so this year it reduced by 2.2 kg)

As you can see, the amount that it reduces by is now different, yet the percentage it reduces by is the same, which is 1-0.977 = 0.023%

Now for why i use 0.25^(1/60) instead of 0.75(1/60), 0.25 stands for, 25 percentage is left after 60 years, while 0.75 stands for 75 percent remains after 60 years,

This is exactly the difference between 0.25^(1/60) and 1-(0.75/60)

I hope this helps you

reinout-gJan 29, 2014

+134

Ok, I got most of that.
But, I'm still wondering why is 0.75 irrelevant? And how do you [^] a number on this page?

VracesJan 29, 2014

+118725

Vraces:
I need to understand why for example
[A radioactive kalashnikov gets less radioactive every year. After 60 years only 25% of the radio-activeness remains. What is the yearly reducing of radio-activeness in percent?]

I'm wondering. Since(Based on my assumption) 0.75^(1/60) should be in english: 75% of of the radioactiveness in one year. Since 75% was removed during 60 years shouldn't 0.75^(1/60) be the answer?[1 - 0.25^(1/60) = 0.75^(1/60)? ] And also. Why should it be ^(1/60) and not the percentage divided by 60?What does ^(1/60) actually mean? What happens when it calculates? I'm aware it multiples itself the times stated. For example: 3^3 = 27 ; 3^3(1/3) = 9 I must understand these things. It's good to know how to solve something, but if you don't know the meaning of it you can't solve another thing. I'm going to guess only Melody could explain this, but others are also welcome. IF you actually know the significance. Do not guess while trying to explain as it would only confuse me. And by the way, I may have confused you a little bit with what I'm trying to say. Good luck and thanks.