Latest Others Aptitude Question SOLUTION: there is a 7 digit telephone no with all different digits. if the digit at extreme right and extreme left are 5 and 6 respectively,find how many such telephone nos are possible

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there is a 7 digit telephone no with all different digits. if the digit at extreme right and extreme left are 5 and 6 respectively,find how many such telephone nos are possible

Asked In Others praveen (11 years ago)

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Dr.Dipin Singh  (11 years ago)

there is a 7 digit telephone no with all different digits. if the digit at extreme right and extreme left are 5 and 6 respectively
then possible numbers are 8*7*6*5*4 = 6720.

Is this solution Helpfull? Yes (16) | No (3)  

Bruce Wayne  (11 years ago)

The digits at the extreme right and left are 5 and 6 resp.
So, the 7 digit number is : 6 _ _ _ _ _ 5
Since repetition of digits are not allowed the second digit can be chosen from (0,1,2,3,4,7,8,9) 8 of the remaining digits. Similarly, the third is chosen from 7, 4 digits is selected from 6 and so on...

So, ANSWER: 8*7*6*5*4 = 6720

Is this solution Helpfull? Yes (10) | No (3)  

Prithivi  (11 years ago)

From the question,
6 _ _ _ _ _ 5
Deals about arrangement(Permutation), we cant repeat the digits..
6 and 5 are already present, remaining digits are 01234789= 8digits
5 spaces are left, hence 8P5=6720

Is this solution Helpfull? Yes (7) | No (1)  

vasu  (11 years ago)

@dipin : u r wrong ,the nums can be repeated so u cant jusz use 8*7*6*5*4

Is this solution Helpfull? Yes (2) | No (4)  

vasu  (11 years ago)

sry m wrng dint read the questn properly

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MONESH ALI SARKAR  (11 years ago)

ans-2520
since leaving extreme right and extreme left no which are fixed(ie,5 and 6)
the rest 5 numbers can be combined in 7p5 ways. therefore answer =2520 on calculating

Is this solution Helpfull? Yes | No (6)  

Mrinal Mahanta  (11 years ago)

answer is 3360
we have to select 5 digit from 8 digits(0,1,2,3,4,7,8,9)
we can select the above as 8c5=56 ways
the five digits can be interchanged among themselves by 5!=60 ways
so answer is 8c5*5!=56*60=3360

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