Question

What will 4 balloons cost if 10 balloons cost £3.00

Answer 1

You can do it proportions
Looks like
10=3
4=x
10x=12\:10
X=1,2<< price of 4 baloons :)

Answer 2

so you will change it into fraction form which is 4/10, which equals .4. and 0.4 time 3 euros equal 1.2 euros per balloon