Hey all, I was working on 7-13 of Hassets' Probability of Risk Management. The problem asked to calculate the difference between the 30th and 70th percentiles of X. The pdf was

f(x) = 2.5*(200^2.5)/x^3.5 for x>200

0 otherwise

I got the answer correct: 93.06

According to my calculation, x0.3 was 323.7289 and x0.7 was 230.6698 But I am really confused: how can the 70th percentile be less than the 30th??? Shouldn't you read the pdf from left to right?

Also, sometimes the interval is closed and sometimes it's open. I know for example when it's 0<=x<=1, you do the integral from 0 to 1. But what about 0<x<1??

Thank you guys and wish everyone a satisfying grade.