Today is 20th March 2011 and it's 9 : 53 P.M. I'm going to write what happened today. The alarm rang at 4 : 00 A.M and I woke up and hurried to turn it off because I didn't want to wake up Isuru's parents by letting the alarm ring continuously. Isuru was sleeping and I tried to wake him up. Then he told me that he wanted to sleep another half an hour. So I continued learning the PS book alone. Isuru woke up at 4 : 30 A.M and we both did some questions together and discussed them.

The discussion was very much helpful where he asked me some questions which are really important and I figured out the answers on my own. For example do you know why the probability of getting an exact value in a continuous probability distribution is zero ? Think about it like this. Imagine the graph of the probability density function. Now the specific area under that particular value is the required probability. To get that area, you have to integrate the probability density function. When you integrate, both the upper and lower limits are equal to that particular value which you want to find the probability. So when you substitute them, the answer becomes zero. I hope you got it.

I came home around 11 : 00 A.M. Despite having a lot of work to do, I watched the movie 'Monsters'. That's my hobby. I can remember when I was doing the final exams of the last semester at SLIIT, even on the day before the exam started I watched a movie. After that I had a nap for around two hours and started the work again.

I completed up to the chapter 6 of that PS Crash Course book and started doing some past papers. I answered some questions in 2010, 2009 and 2008 P&S final past papers. The paper seems to be really easy than I expected. If you know the theories well and if you are good in analytical thinking, then it won't be hard. One thing I realized is that following only the text book is not enough. This PS crash course is really good in that case. For example in 2009 PS final paper, see the last part of the 1st Question. To answer that, you need to know that

E [ X + Y ] = E [ X ] + E [ Y ]

E [ X - Y ] = E [ X ] - E [ Y ]

E [ X . Y ] = E [ X ] . E [ Y ]

E [ c . x ] = c . E [ X ]

Var [ c . X ] = c ^2 Var [ X ]

Var [ X + Y ] = Var [ X ] + Var [ Y ]

Var [ X - Y ] = Var [ X ] + Var [ Y ]

These things are not in the PS text book. But they are in that PS Crash Course Book.

When answering the 1st Question of 2009 final paper, we have to draw a stem and leaf plot. I didn't know how to choose the stem width and leaves so that I used SPSS software to do it for me.

Click on the image to zoom it. See that every leaf is zero.

Then in 2008 final PS paper, Question 1.

A stem and leaf plot is given. Stem width is 10. Here, in between the stem value and leaf value, a decimal point is not given. I have a little bit of confusion here. According to this, to get the values we have to concatenate the stem value and the leaf value and then multiply it by the stem width. Then we get values like 110, 120, 120, 130 .... and so on.

I checked this further by putting some values in SPSS software. Click on the image below to zoom.

My input values were 11, 12, 12, 13, ... and so on. It gave me the stem width 10 and you see a decimal point in between the stem value and the leaf value. I hope to further clarify this at the PS help desk from Hansa sir.

I'll be continuously writing this series of posts until the exams start, so keep in touch with my blog. My instinct tells me what to do next and I simply follow that as I did in previous exams and got good results. So follow me and get good results.

-Tharindu Edirisinghe-

-SLIIT 10'-

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Come here from Malaysia

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