why does size of screen decrease by increasing resolution?

Solution
Screen size and resolution are independent of each other, they are inter-related.

A 21" screen will always be a 21" screen, the screen size does not change at all, but as you increase resolution you put more pixels per inch in the same space making the icons, etc appear to be smaller.
Screen size and resolution are independent of each other, they are inter-related.

A 21" screen will always be a 21" screen, the screen size does not change at all, but as you increase resolution you put more pixels per inch in the same space making the icons, etc appear to be smaller.
 
Solution