To give students an opportunity to work with large numbers.
To give students an opportunity to work on problems that require more than one simple step.
This printable worksheet may be useful: Thousands and Millions
"If I were to ask you to work out answers to these questions, what information would you need to know?"
"Some of these things you can work out from things you already know, some of them need an estimate."
"You're going to be comparing answers with other groups, so make sure that you have written your final thinking carefully, to make it easier to spot differences."
"Each question should be done on a separate sheet of paper."
"If two groups work on the same question and get different answers, it may be because their estimates are different, or it may be because one method is wrong."
How can I ensure that I make reasonable estimates?
The process of adapting difficult problems, "making sense" of them in simpler cases, is a powerful technique for dealing with hard questions. This may be an appropriate moment at which to model this:
Pick one question to work on as a class task.
Ask the students to pose related, smaller questions that they can answer, and build up a body of work (display work?) around the theme, for example:
Then encourage students to work towards the original question.
Which of these questions is the hardest, and why? Have a go at answering it.