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The four digits 5, 6, 7 and 8 are put at random in the spaces of the number below:
3 _ 1 _ 4 _ 0 _ 9 2
a) A four digit number (in base 10) aabb is a perfect square. Discuss ways of systematically finding this number. (b) Prove that 11^{10}-1 is divisible by 100.