1kg costs £1.28. what is the cost of 250g

First, convert 1 kg to g.

1 kg = 1000 g

So 1000 g = 1.28

Set up a proportion:

1000/1.28 = 250/x

Cross multiply:

1000x = 320

Divide 1000 to both sides:

x = 0.32

So 250g costs £0.32