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All of David's telephone numbers have the form 555-abc-defg, where a,

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Math Expert
Joined: 02 Sep 2009
Posts: 55150
All of David's telephone numbers have the form 555-abc-defg, where a,  [#permalink]

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24 Mar 2019, 23:45
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Difficulty:

55% (hard)

Question Stats:

50% (02:32) correct 50% (00:59) wrong based on 10 sessions

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All of David's telephone numbers have the form 555-abc-defg, where a, b, c, d, e, f, and g are distinct digits and in increasing order, and none is either 0 or 1. How many different telephone numbers can David have?

(A) 1
(B) 2
(C) 7
(D) 8
(E) 9

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Joined: 27 Sep 2018
Posts: 37
Re: All of David's telephone numbers have the form 555-abc-defg, where a,  [#permalink]

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25 Mar 2019, 01:02
We can choose only from 2,3,4,5,6,7,8,9 I.e for seven places we can choose from 8 numbers
So different numbers david have= 8C7=8

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Joined: 24 Nov 2018
Posts: 109
Location: India
GPA: 3.27
WE: General Management (Retail Banking)
Re: All of David's telephone numbers have the form 555-abc-defg, where a,  [#permalink]

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25 Mar 2019, 01:11
A, b, c, d, e, f & g are seven digits in increasing order. Neither of which is 0 or 1. So, if a=2, g=8 and when a=3,g=9.
Total number of combinations=2

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Re: All of David's telephone numbers have the form 555-abc-defg, where a,  [#permalink]

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26 Mar 2019, 02:37
given that a,b,c,d,e,f,g are seven digits in increasing order and cannot be 1 or 0 .
So a can take only 2 or 3 -
555-abc-defg : 555-234-5678 or 555-345-6789 only 2 possible .

How come there will be 8 possibilities when its given they are in increasing order ? Please correct me Bunuel
Re: All of David's telephone numbers have the form 555-abc-defg, where a,   [#permalink] 26 Mar 2019, 02:37
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