Kilo means thousand, so if you have 1 kilogram that means you have 1000 grams.
Paulina has a 2.5 kilogram mass, 2 kilograms is 2000 grams.
0.5 means half and to get a half out of anything you have to divide it by 2.
1000 divide by 2 is 500.
Your answer is 2500.