According to the given question one parcel can be posted in 5 ways, that is in either of the one post offices so ⁵C₁. Similarly, for other parcels also it can be posted in ⁵C₁ ways.

Hence the number of ways the parcels be sent by registered post is ⁵C₁ × ⁵C₁ × ⁵C₁ × ⁵C_{1 =} 5 × 5 × 5 × 5 = 625