SOLUTION: A random variable X has the pdf x^2 if 0 < x ≤ 1 f(x) = 2/3 if 1 < x ≤ 2 0 otherwise (a)Find the median of X. (b)Sketch the graph of the CDF a

Algebra ->  Probability-and-statistics -> SOLUTION: A random variable X has the pdf x^2 if 0 < x ≤ 1 f(x) = 2/3 if 1 < x ≤ 2 0 otherwise (a)Find the median of X. (b)Sketch the graph of the CDF a      Log On


   



Question 1203810: A random variable X has the pdf
x^2 if 0 < x ≤ 1
f(x) = 2/3 if 1 < x ≤ 2
0 otherwise
(a)Find the median of X.
(b)Sketch the graph of the CDF and show the position of the median on the graph.

Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!


That's the graph.  Now we'll shade the area under it:



Now we find the area between the graph and the x-axis, take half
of it and find the value of x which divides the entire area into
two parts.

First we find the area under the curved (parabola) part

int%28x%5E2%2Cdx%2C0%2C1%29%22%22=%22%22%22%22=%22%22expr%281%2F3%29%281%29%5E3-expr%281%2F3%29%280%29%5E3%22%22=%22%221%2F3

The right part of the graph is just a rectangle with base 1 and height 2%2F3, 
so its area is just base%2Aheight=%281%29%282%2F3%29=2%2F3.

The entire shaded area is 1%2F3%2B2%2F3%22%22=%22%221

So we need to find the value of x such that half the area 1%2F2 is left of
it and the other half 1%2F2, is on the right of it.

The area under the parabola is 1%2F3 so that leaves 1%2F2-1%2F3=3%2F6-2%2F6=1%2F6 the we must take 
of the rectangle. To get the base of a rectangle with area 1%2F6 that has height 2%2F3, 
we divide the area by the height and get %281%2F6%29%2F%282%2F3%29%22%22=%22%22%281%2F6%29%283%2F2%29%22%22=%22%223%2F12%22%22=%22%221%2F4.  So the
median is 1%2F4 on a unit past 1, or 1%261%2F4.

So the median is 1%261%2F4. To indicate the median, we can draw a green
vertical line through the graph at x=1%261%2F4: 



Edwin