Question

Find the cost of 300g if 1/2kg costs 30p

Answer 1

0.5kg is the same as 500g. 

Let x = the unknown cost of 300g. We will use this to set up a proportion and crossmultiply.

$\frac{500g}{30p} = \frac{300g}{x}$

Now crossmultiply and solve for x.

500x = 300(30)
500x = 9000
x = 18

300 grams cost 18p