To find Julie's weight, we need to subtract 1 kg and 750 g from Peter's weight.
Let's convert Peter's weight to grams:
Peter's weight = 30 kg 500 g = 30,500 g
Now, subtract 1 kg (1000 g) and 750 g from Peter's weight:
Julie's weight = Peter's weight - 1 kg 750 g
= 30,500 g - 1000 g - 750 g
= 28,750 g
Therefore, Julie's weight is 28,750 grams.