He had it in there - as long as you understand that 1&2 are the same button, as are 3&4, 5&6, 7&8, 9&0. So in reality, 0001 and 0002 are the same entries. So for each digit position, you have 5 choices of buttons to hit. So it is 5x5x5x5 = 625 possible combinations. If all 10 digits were separate options, you would…