S1 and S2 DOUBTS HERE!!!!

[astarmathsandphysics]

Try this

[~ Miss Relina ~]

Try this

Thank you Sir .......... but I'm sorry if I disturbed you by asking you plz could you explain the book answer
attached .................what I don't understand is how he get the probability of sticking to the door choosen before and getting the correct door   

[astarmathsandphysics]

There are three doors and initially the probability of picking the correct door is 1/3
After the host picks one of the two not chosen, it is as if the probability of the car being behind the door he has chosen is given to the one remaining unchosen door. so 1/3 +1/3=2/3

[ashwinkandel]

Ann, Barry and Clare are three students taking a multiple choice examination paper. For each question a student has to select the correct answer from five that are offered. For Question 1, Ann has no idea of the correct answer, Barry correctly identifies one answer that is wrong and Clare correctly identifies two wrong answers. All three students decide to guess at random from the answers they think stand a chance of being correct. Calculate the probability that:
a. none of the three students chooses the correct answer.
b. Clare is the only one to choose the correct answer.
c. exactly one of the three students chooses the correct answer.

[astarmathsandphysics]

here

[ashwinkandel]

I have one confusion. For the question attached below, if we are said to draw a cumulative frequency curve, then can we use 100,150,200 on the x-axis of the curve or should we use 100.5,150.5,200.5 as we use the value of Upper Class Boundary while drawing C.F curve. I am really confused.

[Alpha]

I have one confusion. For the question attached below, if we are said to draw a cumulative frequency curve, then can we use 100,150,200 on the x-axis of the curve or should we use 100.5,150.5,200.5 as we use the value of Upper Class Boundary while drawing C.F curve. I am really confused.

You may use 100, 150, 200 etc. You'd use 100.5, 150.5, 200.5 when there wouldn't be an equal sign there. 

[astarmathsandphysics]

Cant see attachement but use 150 etc anyway

[ashwinkandel]

@ astarmathsandphysics you can enlarge the attachment by clicking it. I am still in little confusion. I quote one sentence from my statistics books: "The cumulative frequencies are plotted against the upper class boundaries of the corresponding class." Our class boundary is written in the form x-y where x is inclusive but y is not. However, in the given question 150 200 are inclusive. So, to make it exclusive I add 0.5 and make it 150.5. For this same question mean has also been asked for 4 marks. and it has been done by using 0.5-100.5,100.5-150.5... in the mark scheme.By the way, the full question is from CIE 9709 May June 2011 Paper 61 question no. 6. I also read examiner report. In examiner report the statement was like this: "A mark was awarded for attempting to plot the cumulative frequencies against their respective upper class boundaries"

[Alpha]

@ astarmathsandphysics you can enlarge the attachment by clicking it. I am still in little confusion. I quote one sentence from my statistics books: "The cumulative frequencies are plotted against the upper class boundaries of the corresponding class." Our class boundary is written in the form x-y where x is inclusive but y is not. However, in the given question 150 200 are inclusive. So, to make it exclusive I add 0.5 and make it 150.5. For this same question mean has also been asked for 4 marks. and it has been done by using 0.5-100.5,100.5-150.5... in the mark scheme.By the way, the full question is from CIE 9709 May June 2011 Paper 61 question no. 6. I also read examiner report. In examiner report the statement was like this: "A mark was awarded for attempting to plot the cumulative frequencies against their respective upper class boundaries"

I did that paper some time back. And I got the same confusion as yours.

Yeah, now I get what you mean. You're right. Less or equal to 100 means it stops at 100. So, you cannot use 100 as the starting point for the other class. You have to add 0.5. Make it 100.5.
It's actually the difference between a discrete and continuous variable. The cumulative frequency uses a continuous variable, when you convert it to a simple frequency table, it becomes a discrete variable.

Hope you get me.

And thanks for asking that question. My confusion is cleared, albeit by myself.

[lastgift]

Hi! Doubt in a continuous random variable question.
Q) 5 from this paper attached!

[astarmathsandphysics]

here

[ashwinkandel]

1.
A machine is used to fill cans of soup with a nominal volume of 0.450 litres. Suppose that the machine delivers a quantity of Soup which is normally fistributed with mean x litres and standard deviation y litres. Given that x= 0.457 and y= 0.004, find the probability thata randomly chosen can will contain less than the nominal value.[Ans:0.0401]
It is required by law that no more than 1% of cans contain less than the nominal volume
Find.
i. the least value of x which will comply with the law if y=0.004 [Ans:0.459]
ii. the greatest value of y which will comply wit the law if x= 0.457 [Ans:0.003]

[astarmathsandphysics]

Give me time to get to pc

[ashwinkandel]

One more confusion:

Q. On a particular day, 50% of the employees in a large company had arrived at work by 8.30 am, and 10% had not arrived by 8.55 am.
a. Assuming a normal modal, find the standard deviation of arrival times, in minutes.[Ans:19.50]
b. It is given that only 5% of the employees had arrived by 8.05 am. Without further calculation, explain why this might suggest that normal model is not appropriate [Ans: not symmetrical ... but can you give me explanation..... what is means..]
c. Eighty employees are selected at random. Find the expectation of the number of these employees that arrived between 8.30 and 8.55 a.m.[Ans:32]