1-digit numbers ⇒ We have 1 to 9⇒9 2-digit numbers ⇒xy, we have 9 ways to choose x from 1 to 9⇒9 ways and 9 ways to choose y ( 0 to 9 except x)⇒9*9=81 3-digit numbers ⇒xyz, we have 9 ways to choose x,9 ways to choose y and 8 ways to choose z⇒9*9*8= 648. Total numbers till 1000 without digits repeated in them is 9+81+648=738.