Shubham has to make a telephone call to his friend Nisheeth,unfortunately he does remember the 7 digit phone number But - Maths - Permutations and Combinations

Question

Shubham has to make a telephone call to his friend
Nisheeth,unfortunately he does remember the 7 digit phone number
But he remembers the first three digits are 635 or 674,the number
is odd and there is exactly one 9 in the number The maximum number
of trials Shubham has to make to be successful is a four digit
number of the form abcd then c equal to

Shivam Mishra · Accepted Answer

Dear Student,
Please find below the solution to the asked query:

Let us assume that he starts out with the initials digits as 635
 In that case he wouldhave to work on the following combinatins presuming that he places the number9 first time in the fourth digit and next time in the fifth and then in the sixth and then finallyin the seventh which is necessarily an odd digit so as to make telephone number an odd number
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The total number of combinations with 635 as prefix are324+324+324+729=1701He will have to repeat these 1701 combination with 674 as prefix
So in all, he will have to be prepared to run through 1701+1701=3402 before he can be certain to succeed
Hence c=0 Answer

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