mgmat-palindrome

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pradeepkaushal9518: Legendary Member; Posts: 1309; Joined: Wed Mar 17, 2010 11:41 pmFollowed by: 5 members; Thanked: 33 times

by pradeepkaushal9518 » Fri Jul 16, 2010 4:00 am

A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

40
45
50
90
2500

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Source: Beat The GMAT — Problem Solving | Fri Jul 16, 2010 4:00 am

kvcpk: Legendary Member; Posts: 1893; Joined: Sun May 30, 2010 11:48 pmFollowed by: 7 members; Thanked: 215 times

by kvcpk » Fri Jul 16, 2010 4:06 am

pradeepkaushal9518 wrote:A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

40
45
50
90
2500

Number of positions to be filled is 4.
Numbers that can fill each position are 10 (0-9)

NOw we know that the number is odd.
Hene First position can be filled by (1,3,5,7,9) [5 ways - this will be same as last position]
Now, second position can be filled in 10 ways [0-9] - this will be same as third position.]

Hence count = 5*10 = 50
pick C.

Whats OA?

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pradeepkaushal9518: Legendary Member; Posts: 1309; Joined: Wed Mar 17, 2010 11:41 pmFollowed by: 5 members; Thanked: 33 times

by pradeepkaushal9518 » Fri Jul 16, 2010 4:13 am

correct praveen u have given same explanation as given by the mgmat

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kvcpk: Legendary Member; Posts: 1893; Joined: Sun May 30, 2010 11:48 pmFollowed by: 7 members; Thanked: 215 times

by kvcpk » Fri Jul 16, 2010 4:15 am

pradeepkaushal9518 wrote:correct praveen u have given same explanation as given by the mgmat

good to hear that

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