# percentile help with CDF

• November 6th 2009, 02:14 PM
statman101
percentile help with CDF
I need to understand part b.

how did they get n(p)

in other words, how did they go from
p = F(n(p)) ......to n(p)

see the attachment!
• November 6th 2009, 10:24 PM
matheagle
That's just the quadractic equation. Let x be the $p^{th}$ percentile

so p=F(x) or $p=2(x+{1\over x} -2)$

multiply by x and create a quad equation

$px=2(x^2+1 -2x)$

$x^2 -(2+{p\over 2})x+1=0$

NOW solve for x and discard the bad solution.