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Al, Bertie, Chris and Di have sums of money totalling £150. Al and Bertie have £55 between them and Al and Chris have £65 between them. What is the difference between the amounts that Al and Di have?

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

*This problem is taken from the UKMT Mathematical Challenges.**View the archive of all weekly problems grouped by curriculum topic*