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# How many numbers with 3 different digits can be formed using only the

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Intern
Joined: 08 Jan 2015
Posts: 25
How many numbers with 3 different digits can be formed using only the  [#permalink]

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30 Mar 2015, 10:33
00:00

Difficulty:

15% (low)

Question Stats:

79% (00:52) correct 21% (00:58) wrong based on 72 sessions

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How many numbers with 3 different digits can be formed using only the odd digits?

A. 10
B. 20
C. 40
D. 60
E. 120
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Re: How many numbers with 3 different digits can be formed using only the  [#permalink]

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30 Mar 2015, 12:04
Hi Awli,

This prompt gives us a set of restrictions to work with:

1) Create 3-digit numbers
2) Use ONLY ODD digits
3) NO duplicate digits are allowed

From here, we can use a Permutation to get to the answer:

The digits we're allowed are: 1, 3, 5, 7 and 9

_ _ _

For the first digit, we have 5 options. Once we place a number though, we CANNOT use it again...
For the second digit, we then have 4 options. Once we place a number, we CANNOT use that number again either...
For the third digit, we then have 3 options.

(5)(4)(3) = 60 different 3-digit numbers

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Joined: 06 Nov 2014
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Re: How many numbers with 3 different digits can be formed using only the  [#permalink]

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31 Mar 2015, 01:40
Awli wrote:
How many numbers with 3 different digits can be formed using only the odd digits?

A. 10
B. 20
C. 40
D. 60
E. 120

Odd digits are 1, 3, 5, 7, 9.
We want 3 different digits.
First digit can be chosen in 5 ways.
Second digit can be chosen in 4 ways.
Third digit can be chosen in 3 ways.

Total ways = 5*4*3
= 60
Hence option (D).

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Intern
Joined: 08 Jan 2015
Posts: 25
Re: How many numbers with 3 different digits can be formed using only the  [#permalink]

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31 Mar 2015, 01:45
Thank you very much!
Re: How many numbers with 3 different digits can be formed using only the   [#permalink] 31 Mar 2015, 01:45
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