Divide histogram in three parts

Hi, I want to divide the histogram in three parts and define the ranges of three parts.

minRed = min(red(:));
maxRed = max(red(:));
AvgRed = (minRed+maxRed)/3;
AvgRed2 = AvgRed+AvgRed;

But sometimes the value of AvgRed becomes less than minRed and value of AvgRed2 exceeds the maxRed. What is the correct way to do this?

Answer 1

[Walter Roberson]

A + (B - A) /3 
A + (B - A) /3 *2

[Nataliya]

Suppose minRed = 0.5459 and maxRed = 1. Your solution also gives AvgRed = 0.33 and AvgRed2 = 0.66. Issue still exists

[Walter Roberson]

1-0.5459 is 0.4541. Divide by 3 gives 0.15136. Add 0.5459 gives 0.69726.