There is a seven digit telephone number and 5 and 6 are on extreme right and extreme left. So, the number 0, 1, 2, 3, 4, 7, 8, 9 will lie between these numbers. So, 8C5=
8!
5!3!
=56 We can represent the five numbers in 5! ways = 120 So, numbers of possible telephone number = 120 × 56 = 6,720