All Answers 358512 Answers

Mon 30/11/15

The forum is doing some really weird things.

Last night when I tried to remove threads from my watchlist, and once when I wanted to post a new solution.  The thread was downloaded to my computer instead.

And now, my wrap lantern from yesterday, which is still there if I paste the address straight into the address bar

http://web2.0calc.com/questions/wrap-lantern-sun-29-11-15

Is no where to be seen in the 'questions list' 

This happened to me once before when I was looking for one of Mellie's questions.

Also some of the posts are displaying and then going blank later on.  Anonymous4338 gave a detailed answer to a question, and then the question disappeared.  I mean it was still there but it was just white space.  Weird!!!

Also of coursethe picture insert is not working.  Or, at least, a lot of people have said it is not working. I must not have tried to insert anything since it has been broken.

STRANGER DANGER

http://web2.0calc.com/questions/hey-yall-lt-3#r11

---------------------------------------------

How can you post a picture when the picture upload on the forum is not working properly ?

Thanks very much Alan for these instructions.

http://web2.0calc.com/questions/ven-diagram-need-help-for-questions#r3

Forum / answerer considerations.     Thanks Riddler

http://web2.0calc.com/questions/common-issues

We have a new group of young members.  This is great.  A big welcome to you and to others. :)

And congratulations Riddler on ou 200 points.  I hope you stay long enough to earn 200,000 points :)

http://web2.0calc.com/questions/celebration

http://web2.0calc.com/questions/more-riddles-and-puzzles-for-days#r7

Number puzzle        Thanks Anonymous4338, CPhill and guest :)

http://web2.0calc.com/questions/this-isn-t-a-riddle-it-s-my-8th-grade-math

Simultaneous equations     Thanks Guest.

I thought someone might like to do this one using matrices.  :)

http://web2.0calc.com/questions/math-help_27694

Advanced proof.        Thanks Alan and guest :)

http://web2.0calc.com/questions/help_67408

Absolute inequality     Thanks CPhill

This would be a good one to do a graphing solution too.  I'll do that if I ever get up to it ://

http://web2.0calc.com/questions/can-someone-tell-me-how-to-solve-this-double-absolute-inequality#r1

Exponents equation   These are fun.  Thanks Alan  :)

http://web2.0calc.com/questions/4-x-1-2-x-8_1

Circle problem    Thanks CPhill and Buubleman

http://web2.0calc.com/questions/circle-problem_1#r6

You might prefer the following Melody:

Strictly, dy and dx should be glued together, but we science/engineering types often take liberties with the mathematics!!

Thanks Alan :)

The work done on the spring to get it from 5" to 2" is k*3^2/2

The work done on the spring to get it from 5" to 4" is k*1^2/2

Hence the work done on the spring to get from 2" to 4" is k*(1^2 - 3^2)/2 or -k*(3^2 - 1^2)/2  (it's the work done by the spring that's positive here of course, so the work done on the spring is negative).

Hi Alan and others,

I have only just come back to this question to take a proper look.

Prior to watching you one the forum I never treated calculus dy and dx so much like normal algebra.

To me dy/dx was glued together with super glue.

I guess I understood better when I was studying at university but I do not remember that.

It all makes such perfect sense when you show me how to do things.  

Working through this with you and WolframAlpha as a guide made it so easy.

 BUT, if I come back in a fortninght and try to do it myself I won't be able to.

Isn't that sad. :)

Students often tell me that I do not understand their learning problems, but you see I really do!    

Thanks, i think i figured the answear aready! But i was unsure.

what is 3X + 6???

It is an algebraic expression.

It cannot be simplified and since there is no equal sign there is nothing to solve.  :)

Thanks for letting me know,

It works now :)

@@ What is Happening?  [Wrap4]   Sun 29/11/15   Sydney, Australia Time 9:30 pm   ♪ ♫

A very good day to you all,     

We have had wonderful answers from CPhill, Alan, Heureka, geno3141, Dancer04, Annonymous4338, buubleman, Dragonlance, DragonSlayer554, TitaniumRome, Riddles, Olivia3.141592654, Acer32 and Mattesnillet.  

WOW that is a lot of answerers.  Thank you everyone   

Social report       

I think this must be ther return of the old members week!  Is that because December is nearly upon us?  Lets see, Anonymous4338 has been back for a week or so, DragonSlayer554 returned yesterday, TitaniumRome made his presence felt today.  You three, along with Riddles, Olivia4.14... and Hayley if she is still with us could try and boost the young crowds interest with riddles, puzzles, and quality social threads.  Along with your standard questions and answers of course.

Also Dbg4thebest has posted a new Music report.  I would really like members and guests to support him please.  Thanks Denzel     The post is with the interest posts below. :)

Forum Issues:

There was a problem with posting pictures today.  If this is still a problem tomorrow I intend to send a note off to admin :)

Interest Posts:

If you ask or answer an interesting question, you can private message the address to me (with copy and paste) and I will include it.  Of course only members are able to do this.  I quite likely will not see it if you do not show me.  

1) Music Report #10      Thanks Dbg4thebest       

link dosen't work soz...

Thank you Melody and Alan . 

Yes, thank you very much Alan :)

I think yours was faily intuitive to someone with a lot of maths training. Perhaps you could have said a little more for the extended audience, maybe I could have too, but I think your answer was good.   If anyone askes you or me to explain our answers I know we will be more that happy to oblige. I expect our guests would be happy to oblige too :D

I like the method that you used the best. :)  It was really simple.  :)

We cannot post pics today.  :((

Observations from 

Dragonslayer, CPhill, Alan and myself.

https://web2.0calc.com/questions/system-problem#r5

Thanks Danzel,

I have had a great music day today and I really enjoyed your contributions to it.

I especially liked this one:

Varien- nights in bangalore pt. 2

https://www.youtube.com/watch?v=Jv1E1jYVt2s

I found the instrumentation and voice combination very interesting !

 I would like to seee this performed and get close ups of what is going on.

Do you know if such a clip would exist?

Thank you very much for contributing and for adding to the general appeal of our 'maths' forum   

Thanks, Melody......maybe I should have provided a little more detail........my answer wasn't particularly "intuitive".........just standard Algebra

I like your answer Chris.  Guest 1 and 2 gave good answers too :)

It is a bit unclear what intuitive means to this student or their teacher.

We have all used some algebra.

I took intuitive to mean that we needed to explain the algebra that we were using.  

I think CPhill and guest 2 interpreted it the same way.  :)

A class average mark in an exam is 70. The average of students who scored below 60 is 50. The average of students who scored 60 or more is 75. If the total number of students in this class is 20, how many students scored below 60?

20 in class

mark average is 70

average below 60 is 50

the average of 60 or more is 75

I am going to split the class into 2 groups.  Those who got below 60 (Lower)  and those who got 60 or more.(Upper)

I do no know how many are in each group but I do know that there are 20 students altogether so the lower+upper  =20

The average of the lower marks is  50      so   sum of lower marks  is 50L

The average of the upper marks is  is  75      so   sum of upper marks  is 75U

Now there are 20 students and the average mark is 70

so     (50L+75U)/20   =70

50L+75U   =70*20

2L+3U=(70*20)/25

2L+2U+U=56

But 2L +2U=2* all the students = 40

40+U=56

U=16

There are 16 studens in the top group so there must be 4 students in the top group.

Answer: 4 students scored below 60. 

Let the number of students who average  50 = x

Let the number of students who averaged  75 = 20-x    

And we know that :

[ 50x  + 75(20-x)] / 20  = 70     simplify

50x + 1500 - 75x   =   1400

100 = 25x     divide both sides by 25

4 = x    this is the number that averaged 50  [ below 60]

w + 8 = -3      subtract 8 from both sides

w  =  -11

Thanks, Guest.....don't forget, the minus sqrt of 144 must also be included, i.e., -12 is the other answer

Thanks Dragonlance, the last bit confused me.  I'll think about your answer  :)

5.    The probabilities for Elizabeth and Edward to choose Business as their major are 0.8 and 0.3, respectively. 

Find the probability that:

a).    Both choose Business as their major.

P = ( both choose Business as their major ) = (0.8) . ( 0.3) = 0.24    yes

b).     Neither chooses Business as their major.

P = ( Neither chooses Business as their major ) = (0.2) . ( 0.7) = 0.14    yes

c).    Only Elizabeth chooses Business as her major.    

          = ( This means Elizabeth does Business and Edward does NOT do business) = 0.8*0.7 = 0.56

So our guest#1  was totally correct!

Hi Buubleman :)

Draw a right angled triange.

put theta in one of the acute angles.

cos theta = 5/13

So adjacent side is 5 and the hypotenuse is 13

Us pythagotean theorum to find the opposite side and it is 12

now you should be able find all the rations and put them together as you hve been asked :) 

Well DS, now that you are back you cano come here when you are bored and learn some cool maths... or help some other kid lean. 

Also, you are a good artist arn't you?  Well when the picture feature is working again you can show us some of your work :)