In simplest form, it is like attempting to find the combination to a digital lock. If you find the combination you get the reward. You may or may never find the combination depending how many characters are in the password (difficulty). By bringing your friends on board with you and joining your effort your chances increase. The more friends that you have helping out the faster you will find the combination (statistically). You agree to split the reward, when found, by taking the total number of attempts made by the group and dividing out the winnings. In other words, to find your reward: Reward / total attempts made * number of attempts you personally made. So to answer your question, all you need is one worker (machine) to get the job done. Numbers is what gets that same job done expeditiously.