The whole pie chart represents 100% of the percentage.
Also, the circle has an angle of 360 degrees.
We can use the rule of three to find the percentage of category 2.
Then:
100%------------------- 360 degrees
x ------------------------- 72 degrees
where x= (100*72) / 360
x = 20 degrees
Hence, the percentage for category 2 is 20%
Now, we need to find which category contains exactly 30%
If we assume that cat 2 + cat 3 represents 50% of the percentage.
Then, the 50% of 360degrees is 180degrees.
Then:
cat 2 + cat 3 = 180
72 + cat 3 = 180
Solve for cat 3
cat 3 = 180 - 72
cat 3 = 108 degrees
So, we can use the rule of three to get the percentage:
100%------------------- 360 degrees
x ------------------------- 108 degrees
where x = (100*108)/360
x = 30%
Hence, category 3 represents 30%.