Easily Even

Find the number of even 4 4 digit numbers that can be formed from the digits 1 , 2 , 3 , 4 , 5 1,2,3,4,5 without repetition of any digit.


The answer is 48.

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4 solutions

Ivan Sekovanić
Jul 19, 2014

This problem can be basically rephrased into looking for all the ways to put the 5 5 digits into 4 4 places, so the that last place can only be a 2 2 or a 4 4 . Therefore, we get:

1 1^{\circ} For the last digit we have 2 2 possible options (either 2 2 or 4 4 ).

2 2^{\circ} For the second digit (from the right) we have 4 4 possible options (since repetition is not allowed and we already used one digit).

3 3^{\circ} For the third digit (from the right) we have 3 3 possible options (same as above, we already used two digits).

4 4^{\circ} For the fourth and final digit (from the right) we have 2 2 possible options (since we already used 3 3 out of 5 5 digits).

Thus, to sum up, the total number of combinations (and number of such integers) is 2 4 3 2 = 48 2\cdot 4\cdot 3\cdot 2 = \boxed{48} .

Radha Krishnan B
Jul 18, 2014

No of numbers possibly formed is 5! = 120. Probability last digit is even is 2/5. So no if such numbers is 2/5*120=48.

Nice :) .....

Krishna Ar - 6 years, 10 months ago

I didn't think of this. Nice! Word "Krishna" really has something special to do!!

Kartik Sharma - 6 years, 10 months ago

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What did you mean by that? :-o

Krishna Ar - 6 years, 10 months ago

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It was just a joke as you might be knowing that I love to crack jokes.

I actually meant to say that as this problem was posted by KRISHNA Ar and the solution was posted by Radha KRISHNAn B. Therefore, KRISHNA really has some importance than the name of a GOD. By the way, this is not the only time I observed the person Krishna being an AWESOME man.

Sorry to both if you didn't like that but you should be proud of it!!! ;)

Kartik Sharma - 6 years, 10 months ago

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@Kartik Sharma Too complicated a thinking

Agnishom Chattopadhyay - 6 years, 10 months ago

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@Agnishom Chattopadhyay Thou thinkest the unthinkable -_-

Krishna Ar - 6 years, 10 months ago

@Agnishom Chattopadhyay @Agnishom Chattopadhay Is that a compliment? Also, you @Krishna Ar , is that a compliment?

Kartik Sharma - 6 years, 10 months ago
Adir Krafman
Jun 18, 2016

Since we know the last digit must be 2 or 4 (two options), we multiply the number of possible arrangements of the four other digits (4!) by 2. => 4!*2 = 48

Paola Ramírez
Jul 15, 2015

4 × 3 × 2 × 2 = 48 4\times3\times2\times 2=\boxed{48}

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