Practice

Practise until it sticks

Choose a topic, a skill or a difficulty. Calculation exercises have new versions with fresh numbers once you have solved them, so you can practise the method rather than memorise an answer.

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Practice, difficulty 2 of 3

Identify the population

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A city's transport department wants to know how many minutes residents spend travelling to work. It mails a questionnaire to 2,000 addresses chosen at random from the electricity billing list; 1,140 are returned. What is the population of interest?