A group of people went to a coffee shop. Each person chose a drink and a treat.
Drink
Coffee
Treat
Muffin
Tea
Tart
number of people who chose coffee: number of people who chose tea = 1:4
Of those who chose coffee,
number of people who chose a muffin: number of people who chose a tart = 2:7
Of those who chose tea,
number of people who chose a muffin: number of people who chose a tart = 5:1
What fraction of the people chose a tart?
You must show how you get your answer.