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There is a 7-digit telephone number with all different digits. If the digit at extreme right and extreme left are 5 and 6 respectively, find how many such telephone number are possible ?
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- 120
- 100000
- 6720
- 30240
- None of the above
Correct Option: C
There is a 7 - digit telephone number but extreme right and extreme left positions are fixed .
i. e. , 6 x x x x x 5
∴ Required number of ways = 8 x 7 x 6 x 5 x 4 = 6720
