Grandma bakes a cake for her grandchildren who are going to visit her.
She has forgotten whether $3$, $5$ or all $6$ of her grandchildren will visit.
She wants all of the cake to be eaten by her grandchildren and would like each grandchild to get the same amount of cake.
To prepare for all three possibilities, what is the smallest number of pieces into which she should cut the cake?
If you liked this problem, here is an NRICH task
which challenges you to use similar mathematical ideas.