500
Two families go to the cinema.
The Smith family buy tickets for one adult and four children and pay £19.
The Jones family buy tickets for two adults and two children and pay £17.
What is the cost of one child's ticket?
£3.50
adult + child is £17 ÷ 2 = £8.50
adult + 4 children is £19, so 3 children cost £10.50,
so 1 child costs £10.50 ÷ 3