It can be 0... That's a fact.

It's a tricky question because there are factors involved like Mining difficulty and the total hashing power on the network... The 10 minutes is a constant written on the Bitcoin code, but the ones who find the block are the miners, so, if the difficulty is high and the hashing power is low, the probability of finding 3 blocks in 10 minutes is lower than the case where the hashing power is high.