Permutations

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amit.lohchab: Junior | Next Rank: 30 Posts; Posts: 10; Joined: Sun Jul 24, 2011 10:24 pm

by amit.lohchab » Fri Nov 18, 2011 12:48 am

38. How many positive integers less than 10,000 are there in which sum of digits equals 5?
(a) 31
(b) 51
(c) 56
(d) 62
(e) 93

Answer - 56

Source: Beat The GMAT — Problem Solving | Fri Nov 18, 2011 12:48 am

neelgandham: Community Manager; Posts: 1060; Joined: Fri May 13, 2011 6:46 am; Location: Utrecht, The Netherlands; Thanked: 318 times; Followed by:52 members

by neelgandham » Fri Nov 18, 2011 2:25 am

Already answered, and done brilliantly by Brent@GMATPrepNow and Saketk https://www.beatthegmat.com/very-tricky- ... 25349.html

Anil Gandham
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user123321: Master | Next Rank: 500 Posts; Posts: 385; Joined: Fri Sep 23, 2011 9:02 pm; Thanked: 62 times; Followed by:6 members

by user123321 » Fri Nov 18, 2011 4:06 am

we need to get all positive integers less than 10000.
=> all integers less than or having four digits.
(n+r-1)C(r-1)
=>8C3 = 56

user123321

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