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Obviously?
Age 14 to 18
Challenge Level 
Why do this problem?
As a simple exercise using modulus arithmetic where learners can make and test their own conjectures. By trying small values of n learners may make their own conjectures about when the expression is divisible by 6 and when it is not.Key question
How can we write the expression as an equivalent expression modulo 3?You may also like
Old Nuts
In turn 4 people throw away three nuts from a pile and hide a quarter of the remainder finally leaving a multiple of 4 nuts. How many nuts were at the start?