{statics} Kvartil (quartiles) why I didnt get right solution ?

[artiny]

Homework Statement

On this vector I didnt get the right answer:

x = [ 5 8 10 11 137 ] [/B]
q3: i = (p/100)*n = (75/100)*5 = 3.75 >> 4th in vector is 11
q1: i = (25/100)*5 = 1.25 >> 2nd is 8

in MATLAB is solution

Homework Equations

The Attempt at a Solution

 

[haruspex]

Never seen this concept before, but from a little reading at http://au.mathworks.com/help/stats/quantiles-and-percentiles.html it seems that the vector is interpreted as:
1/10 are <= 5
3/10 are <= 8,
5/10 are <= 10
etc.
For the first quartile, we want find how many are <= 0.25. This is done by interpolation between1/10 and 3/10. 0.25 is positioned (0.25-0.1)/(0.3-0.1) along that interval, so gets that share of (8-5):
5 + (8-5)*(0.25-0.1)/(0.3-0.1) = 7.25.