Given:8 digit telephone number starts with 270 .

To find: How many 8-digit telephone numbers can be constructed?

There are 10 digits between 0 to 9,and three of them are utilized in filling up the first three digits i.e.270 of the 8 digit phone number,so remaining number of digits=10-3=7,and this need to be used in filling up the remaining 8-3=5 places of the telephone number.

i.e.the remaining 5 places need to filled up with any one of:1,3,4,5,6,8,9

So, number of ways=7 × 6 × 5 × 4 × 3=2520.