Hannah and Will from Tattingstone School and Carolyn from St Monica School sent us very clear solutions to this problem. The explanations in brackets were written by Carolyn:

4 x 60 = 240 litres an hour (I multiplied 4 by 60 because there are 60 minutes in an hour)
240 x 24 = 5 760 litres a day (I multiplied my answer by 24 because there are 24 hours in a day)
5 760 x 365 = 2 102 400 litres a year (I multiplied that answer by 365 because there are 365 days in a year)

70 x 60 = 4 200 beats an hour (I multiplied 70 by 60 because there are 60 minutes in an hour)
4 200 x 24 = 100 800 beats a day (I then multiplied my answer by 24 because there are 24 hours in a day)
100 800 x 366 = 36 892 800 beats in a leap year (I multiplied that answer by 365 because there are 365 days in a year)

Christopher from St Gerardine's Primary School answered the last part:

To work out the third question divide 500,000 by 24 and then by 365.
The answer is roughly 57.

In fact, Will from Tattingstone correctly concluded that the person is just over 57.