Ten balls are identical in size and shape of which 2 are red, 3 are blue and 5 are green. The two red balls are labelled as '1' and '2', the three blue balls are labelled '1', '2' and '3', and the five green balls are labelled '1', '2', '3', '4' and '5'. Find the number of ways of choosing 2 balls of identical colours.

5x4+3x2+2x1=28

but answer is 14... what is wrong with my workings?