Melody

Repair job     

(a) It is noted that 8% of students are left handed. If 20 students are randomly selected, calculate the

i. probability that none of them are left-handed,

0.92^20 = 0.18869

 ii. probability that at most 2 are left-handed,

zero one or two are left handed

=           0.92^20          +   20 * 0.92^19 * 0.08  +    20C2 * 0.92^18  *  0.08^2

=     0.188693329     +      0.328162311     +               0.271090605

= 0.81648

  iii. standard deviation for the number of left-handed students

Don't know, I would have to research this one.

http://www.dummies.com/how-to/content/how-to-find-the-mean-variance-and-standard-deviati.html

p=0.08    q=0.92   n=20

I think this stays the same as before.

\(\sigma=\sqrt{np(1-p)}\\ \sigma=\sqrt{20*0.08*0.92}\\ \sigma\approx 1.21326\)

(b) If 50 classes of 20 students are randomly selected, what is the probability that 10 classes have no left-handed students? (10 have all right ahanders and the other classes do no have all right handers.

I think

50C10 * (0.92^20)^10 * (1-0.92^20)^40 = 0.137 

(all final answers are approximation. )

Nov 20, 2015 12:22 PM

Yes, you are right - I'll have to wear my glasses next time LOL    Thanks  

I will one of these days, though I have enjoyed  'Shadow Guesting' for some time.  I wonder.... Is it easier to edit your answers as a member?  I often go back to add more info or fix a typo and I have to repost the whole thng.   How about 'pasting' ?    How about that annoying reCaptcha "i am not a robot" authenticity checker...does it go away?  (THAT would make it worthwhile!! ha)

~jc

Hi jc                 (that is an edit,  LOL  )

I have only ever heard one member complain that she sometimes has trouble editing. I have NEVER had any trouble at all except with regards to LaTex.  Sometimes LaTex gets 'sticky'

I get the "I am not a robot " thing if I start a new thread but it NEVER comes up when I am just answering someone elses question.

We would like you to join.   

Will 85237 answered your question.

He in not a guest !   He is a member !!

And you are right.  Will gave a very good answer to this question.  Thanks Will     

I am sure Will was very pleased to receive your recognition.  Thanks :)

490 are left in Seville.  LOL    

A square and an equilateral triangle have the same perimeter. Let Abe the area of the circle circumscribed about the square and B be the area of the circle circumscribed about the triangle. Find A/B

Let the perimeter be 12p

So the sides of the square are 3p each and the sides of the triangle are 4p each

\(A \div B = \frac{4.5\pi p^2}{1}\div \frac{16p^2\pi}{3}\\ A \div B = \frac{4.5\pi p^2}{1}\times \frac{3}{16p^2\pi}\\ \frac{A}{B} = \frac{4.5}{1}\times \frac{3}{16}\\ \frac{A}{B} = \frac{4.5*3}{16}\\ \frac{A}{B} = \frac{13.5}{16}\\ \frac{A}{B} = \frac{27}{32}\\ \)

Sun 22/11/15

1) How do members score points and edit posts?      Thanks for asking Riddler  

http://web2.0calc.com/questions/points_1#r6

2)  Riddler invites you to post fun-facts.  Thanks Riddler  

Can you add to the fun facts. ??

http://web2.0calc.com/questions/fun-facts

3)  Proof involving sum of squares and prime numbers  NOT ANSWERED.  

http://web2.0calc.com/questions/sum-of-two-square-as-prime

4) Mellie questions (repeated) - geometry   Lots of incircles and circumcircles.  Really interesting questions 

I think they have all now been answered by either CPhill or myself.    

a) http://web2.0calc.com/questions/a-square-and-an-equilateral-triangle-have-the-same-perimeter-let-abe-the-area-of-the-circle-circumscribed-about-the-square-and-b-be-the-area-of-the-circle

b) http://web2.0calc.com/questions/let-m-be-the-midpoint-of-side-ab-of-triangle-abc-angle-bisector-of-ad-of-angle-cab-and-the-perpendicular-bisector-of-side-ab-meet-at-x-if-ab-40-and-mx-9

c) http://web2.0calc.com/questions/find-the-circumradius-of-triangle-jkl-if-kl-16-and-jk-jl-17

d) http://web2.0calc.com/questions/find-the-inradius-of-triangle-jkl-if-jk-jl-17-and-kl-16

e) http://web2.0calc.com/questions/let-ab-6-bc-8-and-ac-10

@@ What is Happening?  [Wrap4]   Sat 22/11/15   Sydney, Australia Time 12:07am (Really Sunday)  ♪ ♫

Hi all, 

There has been 2 days worth of great questions and answers.  Our intrepid answerers were Alan, CPhill, Heureka, Syakirah159, Dragonlance, Twisted2017, adylyn_rae, TMga2yb, Shaniab29544, Bracefaceshae, Rom, Mathkid, Mellie, Will85237 and many guests.  Thank so much.  Without our wonderful answerers this forum would not exist.   

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)  It is really good to see young people playing on the forum again - it has been a while.

Unfortunately you are all guests.  Please join up or at least use names in your posts so that people can get to know you.  You will find it a lot better that way, really you will.   

how far will a car travel in 3 hours 15 minutes at an average speed of 60mph 

3hr 15min = 3 1/4 hours  = 3.25  hours

speed = distance / time

60=d/3.25

multiply both sides by 3.25 :)

Can anyone loan me their glasses please.

I definitely need different - better ones tonight  !!!    LOL