In the following Venn diagram, the pentagon stands for 'Librarians', the rectangle stands for 'Income Tax Payers', and the circle stands for 'Post-graduates'. The given numbers represent the number of persons in that particular category.

How many librarians are these who are also post-graduates?

55

The pentagon stands for 'Librarians',

The rectangle stands for 'Income Tax Payers',

The circle stands for 'Post-graduates'.

Step 1 ) Look at the figure of pentagon , circle and rectangle

Step 2) Look at  number given in the figure as the librarians are these who are also post-graduates

Step 3) By visual observations we conclude that (30 + 25 = 55 ) is the number which represents the librarians who are also post-graduates