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Sunday, January 27, 2008
GRE MATH PROBLEM OF THE DAY
The number of five 5-digit telephone numbers having at least one of their digits repeated is A) 90000 B) 10000 C) 30240 D) 69760 E) None of these
here the logic is appllied of permutation combination 10^5 means at every digit there are 10 possibilities like there are five digit A B C D E every digit having 10 possibilities and we sustract from 10^5 are 10*9*8*7*6 because these digits having no repetation hence the result is that if we do 10^5-10*9*8*7*6 then we get the result 69760 means these are number in which atleast one digit would be repeated...........Kuldeep
D is d ans i got
ReplyDeleteit seems to b 69760...
ReplyDeleteis it right?
it seems to b 69760...
ReplyDeleteis it right?
it seems to b 69760...
ReplyDeleteis it right?
hey... u r ryt.. the answer id 69760
ReplyDeleteIt's 10^5 - 10x9x8x7x6
ReplyDeleteatul how is it 10^5?
ReplyDeletethey say repeat only 1ce?
it should be 69760
can u explain in detail. i am unable to catch it
ReplyDeletehere the logic is appllied of permutation combination 10^5 means at every digit there are 10 possibilities like there are five digit A B C D E every digit having 10 possibilities and we sustract from 10^5 are 10*9*8*7*6 because these digits having no repetation hence the result is that if we do 10^5-10*9*8*7*6 then we get the result 69760 means these are number in which atleast one digit would be repeated...........Kuldeep
ReplyDeleteNumber of digits=5
ReplyDeleteMax possibilities for each digit= 10 (from 0 to 9)
Max possible numbers from 5 digits= 10x10x10x10x10=10^5.....(1)
Max Possible numbers in which there is not a single reptition=
10x9x8x7x6.................(2)
If you will subtract (2) from (1), you will get the max numbers of 5 digits which have atleast one repetion.
10^5-10x9x8x7x6=69760
Abhishek
the questions said : "The number of five 5-digit telephone numbers having at least one of their digits repeated is"..
ReplyDeleteat least one of the digits repeated means it can have more than one digit repeated...
so the anwser would be
9*10*10*10*10 = 90000
5th place can be filled with all digits except zero so 9..and the following places can be filled with any of the 10 digits..
meghna said that, first place cant b filled with zero, but telephone number can be filled with zero cause zero is correct for telephone number.
ReplyDeleteI am going for a professional to solve this critical problems.
D is correct 10^5
ReplyDeleteWhy are 10,9,8,7,6 the numbers that are not repeated?
ReplyDeleteWhy are 10,9,8,7,6 the numbers that are not repeated?
ReplyDeleteWhy are 10,9,8,7,6 the numbers that are not repeated?
ReplyDelete