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How many 4 digit numbers begin with a digit that is prime

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Senior Manager
Joined: 14 Aug 2006
Posts: 365
Followers: 1

Kudos [?]: 3 [0], given: 0

How many 4 digit numbers begin with a digit that is prime [#permalink]  16 Oct 2006, 21:24
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Difficulty:

(N/A)

Question Stats:

100% (01:47) correct 0% (00:00) wrong based on 1 sessions
How many 4 digit numbers begin with a digit that is prime and end with a digit that is prime

A)16
B)80
C)800
D)1440
E)1600
Manager
Joined: 30 Jun 2006
Posts: 87
Followers: 0

Kudos [?]: 4 [0], given: 0

E for me.

The units place can be filled ini 4 ways ( 2, 3 ,5,7)
The tenth and the hundreds place can each be filled in 10 ways ( 0,1,2 ... 9)
The thousands place can be filled ini 4 ways ( 2, 3 ,5,7)

Hence the number of required numbers are 4 * 10 * 10 * 4 = 1600

Hope this to be correct.
Manager
Joined: 12 Sep 2006
Posts: 92
Followers: 1

Kudos [?]: 2 [0], given: 0

E for me as well, same reasoning as jainvik7

what is the OA?
Senior Manager
Joined: 14 Aug 2006
Posts: 365
Followers: 1

Kudos [?]: 3 [0], given: 0

OA is E..
What about the numbers that are repeated, though?

like 2112 or 2222 and so on..?
Director
Joined: 23 Jun 2005
Posts: 847
GMAT 1: 740 Q48 V42
Followers: 5

Kudos [?]: 29 [0], given: 1

E

Possibilities for the first digit 4; last digit 4;the other two digits 10

4*4*10*10 = 1600
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