10 prime factors to 2*5

8 prime factors to 2*4

...ok, the wording in this question is ambiguous... the problem should probably end with "What is the least number of buns such that every hot dog has a bun and every bun has a hot dog."

multiply the unique prime factors together:

2*5*4 = 40

40/8 = 5 packets of buns

40/10 = 4 packs of hot dogs