A three-digit code for certain logs uses the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 according to the following constraints. The first digit cannot be 0 or 1, the second digit must be 0 or 1, and the second and third digits cannot both be 0 in the same code. How many different codes are possible?
first digit has 8 possibilities. 2~9 if second digit is 1, then third digit has 10 possible values. that gives us 8 x 10 = 80 if second digit is 0, then third digit has 9 possible values, and that gives us 8x9 = 72
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2010-1-22 11:12:00
收藏
收藏
楼主