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# S2 Cumulative freq Watch

1. http://www.examsolutions.net/a-level...June/paper.php

For question 7B can someone explain how I would do the '1/5' part ?

the method I use is to integrate the first function =0 and sub in the lower limit. Next I would integrate the last function =1, and sub in the larger limit.
2. (Original post by imran_)
http://www.examsolutions.net/a-level...June/paper.php

For question 7B can someone explain how I would do the '1/5' part ?

the method I use is to integrate the first function =0 and sub in the lower limit. Next I would integrate the last function =1, and sub in the larger limit.
I think I kind of see what you said there but not 100% sure what it is or what it achieves - would you mind clarifying please?
3. (Original post by SeanFM)
I think I kind of see what you said there but not 100% sure what it is or what it achieves - would you mind clarifying please?
For example if we're given f(x)=1/5 with limits 1<x<4

to find F(X) i would do integrate it and make it =0 and sub in the lowest limit.

1/5x+c=0 (integral)

sub in 1 (lowest value) and solve for C

c= -1/5
4. (Original post by imran_)
For example if we're given f(x)=1/5 with limits 1<x<4

to find F(X) i would do integrate it and make it =0 and sub in the lowest limit.

1/5x+c=0 (integral)

sub in 1 (lowest value) and solve for C

c= -1/5
Ohh, I see what you mean, and it's kind of like the opposite... interesting method, but you could do it a bit better.. (I think)

So for x^2/45, you integrate between x and the lower limit to find the CDF for that region.

The middle bit, you also integrate between x and the lower region (which basically is finding F(x) - f(3), so it only takes the probabilities in that region, so to find the CDF (remember that F(x) means the probability of f being x or less) you need to add F(upper limit of previous region), which makes sense if you think about it, because you're basically combining the probability of a value being between 3 and x, plus the probability of the value being less than 3, which adds together to give probability of X being less than x. In notation, that's .

And you can use a similar logic for the third part (and 'joining it' on to to the second part, which already has the first part joined.

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Updated: June 25, 2016
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