I have data that looks like this

Product name Category Score Rank score by category
EM 1 CAMERAS 45 4
EM 2 CAMERAS 46 3
GX 1 CAMERAS 50 1
GX 2 CAMERAS 47 2
iphone PHONES 50 1
samsung s5 PHONES 45 3
nexus 5 PHONES 49 2

I need an equation which will rank scores within each category.

Does anyone have any ideas?