How quickly can you figure it out?

Halloween has finally arrived and with it comes a mathematical brain teaser that left us scratching our heads for a good while. *Considers using it on trick or treaters tonight* The lovely folk at A Fun Zone gave us this problem to deal with, and as much as we love chocolate, it took us a while to work it out… Have a look: “Halloween was almost over, and Mr Green had less than 20 sweets left. When the doorbell rang, he thought he would give all the sweets away. “When he opened the door, there were two trick or treaters. He wanted to give away the sweets evenly, but he noticed that when he divided the sweets in two, there was one left over. “At that point, he saw another trick or treater behind the first two. Again, he tried to divide the sweets evenly among the three of them, but again one was left over." “Finally, another trick or treater came to his door, making it four trick or treaters altogether. Mr. Green still had one sweet left over after dividing the left over sweets into fours. “So how many sweets did Mr. Green have left when the doorbell rang?” There’s a reason we weren’t the best at maths in school… If you haven’t figured it out, the answer is way (WAY) down below… ….           ….         ….           ….           ....             SOLUTION: Mr. Green had only 13 sweets left when the doorbell rang. 13 is one more than 12, which is divisible by two, three and four. Simple now you know it right?