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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote Odd 3-digit numbers This topic has 2 member replies Odd 3-digit numbers This could be a repeat. I couldnt dig up an older matching topic though. How many odd 3-digit integers greater than 800 are there such that their digits are different? A)40 B)56 C)72 D)81 E)104 OA - C)72 I could find the answer by actually browsing through the 100 odd numbers between 801 and 999 included. I'm sure there's a shorter way. Can anyone help me with this? Legendary Member Joined 20 Jun 2007 Posted: 1153 messages Followed by: 2 members Upvotes: 146 Target GMAT Score: V50 lali_mew wrote: This could be a repeat. I couldnt dig up an older matching topic though. How many odd 3-digit integers greater than 800 are there such that their digits are different? A)40 B)56 C)72 D)81 E)104 OA - C)72 I could find the answer by actually browsing through the 100 odd numbers between 801 and 999 included. I'm sure there's a shorter way. Can anyone help me with this? Here is the process: for first digit we have 2 options (8,9) for second digit we have 9 options (1,2,3,4,5,6,7,8,9,0)=10-1(which is used in the first option) = 9 for third digit we have 5 options (1,3,5,7,9). we have to place 1 at the third digit. 2*8*1 = 16 first place can be arranged in two ways (8,9) third place can be arranged in one way (1) second place can be arranged in 8 ways. Similarly we can arrange all the the three remaining odd integers i.e 3,5,7 16*4 = 64 we have to place 9 at the third digit. 1*8*1 = 8 first place can be arranged in one way (8) third place can be arranged in one way (9) second place can be arranged in 8 ways. 64+8 = 72 Let me know if you have any doubts. Junior | Next Rank: 30 Posts Joined 15 Aug 2008 Posted: 12 messages Parallel_chase. That was brilliant. Thanks a lot! • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

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