Given : 0 to 9 digits (i.e., 10 digits)
To find : number of 5-digit telephone numbers
There are 10 digits form 0 to 9 out of which 6 and 7 are fixed in first and second places respectively. Since the repetition of digits is not allowed, therefore the third, fourth and fifth places can be filled in 8, 7 and 6 ways respectively.
Hence five places can be filled in 8 x 7 x 6 ways i.e., 336 ways Required number of telephone numbers = 336
