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A palindrome is a number that reads the same forward and backward. For

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A palindrome is a number that reads the same forward and backward. For  [#permalink]

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New post 23 Jan 2020, 01:12
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A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

57% (01:00) correct 43% (01:40) wrong based on 21 sessions

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Re: A palindrome is a number that reads the same forward and backward. For  [#permalink]

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New post 23 Jan 2020, 04:16
Bunuel wrote:
A palindrome is a number that reads the same forward and backward. For example - 1331. How many 4-digit palindromes can be formed using two of the five digits - 1, 3, 5, 7, and 9?

A. 10
B. 20
C. 30
D. 40
E. 60


FIve digits given: 1, 3, 5, 7, and 9

2 out of 5 digits can be chosen in 5C2 = 10 ways

Palindrome for any two chosen digits a and b can be made in two ways i.e. abba and baab

Total favourable outcomes = 5C2*2 = 10*2 = 20 ways

Answer: Option B
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Re: A palindrome is a number that reads the same forward and backward. For  [#permalink]

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New post 23 Jan 2020, 04:24
1
Bunuel wrote:
A palindrome is a number that reads the same forward and backward. For example - 1331. How many 4-digit palindromes can be formed using two of the five digits - 1, 3, 5, 7, and 9?

A. 10
B. 20
C. 30
D. 40
E. 60


Let the 4 digit be ABCD
Number of options for A = 5
Number of options for B = 4 {Note that, 2 digits have to be used out of 5 available, A & B have to be different]
Number of options available for C & D = 1 each
--> Total number of selections possible = 5*4*1*1 = 20

Option B
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Re: A palindrome is a number that reads the same forward and backward. For  [#permalink]

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New post 24 Jan 2020, 05:56
we can take 2 number from 5 numbers in 5c2 ways, each pair has again 2 possibilities, so 2*5c2 = 2*10 = 20 ways.
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Re: A palindrome is a number that reads the same forward and backward. For   [#permalink] 24 Jan 2020, 05:56
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A palindrome is a number that reads the same forward and backward. For

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