how to calculate the probability under a pdf curve and divide it into different sections (areas)?

I have a few probability plots both pdf and cdf such as weibull or gaussian probabilities. the x axis is between some numbers. I divide the pdf plot into different parts (four parts). when how can i find the area underneath each of this sections? the some of all four sections should be 1.

[Petar Pavic]

did you manage to solve it?

Answer 1

[Udit Gupta]

Assuming you have the curves as a matlab vector, you can use the trapz function to find area under it.

See http://www.mathworks.com/help/matlab/ref/trapz.html