Joan makes cups of tea and coffee at a lunch club Each cup requires 250 ml of boiling water.
She has a kettle that boils up to 1.7 litres of water each time.
She boils 10 litres of water in an urn.
She then uses the kettle to boil the rest of the water she needs.
Find the least number of times that Joan needs to boil the kettle to make 56 cups.
Show how you decide.