Alison has a set of ten fridge magnets showing the integers from to inclusive. In how many different ways can she split the set into five pairs so that the sum of each pair is a multiple of ?
(A) (B) (C) (D) (E)
Alison has a set of ten fridge magnets showing the integers from to inclusive. In how many different ways can she split the set into five pairs so that the sum of each pair is a multiple of ?
(A) (B) (C) (D) (E)