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![[Post New]](/templates/default/images/icon_minipost_new.gif) 25 Feb 2008 22:50:56 IST
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A person writes letters to 4 friends and addresses the corrs. envelopes.In how many ways can the letters be placed in the envelopes so that atleast 2 of them are in wrong envelopes? I have done it by 2 methods....but both answers r not matching.........now u have to tell me where I m wrong. Ist method total no. of ways : 4 ! no. of ways in which all r correctly placed : 1 no. of ways in which 1 is wrongly placed and 3 r correctly placed : 0 so, no. of ways in which atleast 2 r wrongly placed : 4! - 1- 0 = 23 IInd method no. of ways in which atleast 2 r wrongly placed = no. of ways in 2 r wrongly placed + no. of ways in which 3 r wrongly placed + no. of ways in which all r wrongly placed. = 2 + 1 + 9 = 12 so, my both answers r not matching........ may b I hav done a silly mistake , but I m unable to locate it ......... so, pls help me out!!!!!!!!!!!!
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LOKESH SARDANA,
department of Production and Industrial engineering,
Indian Institute of Technology,Roorkee.
Happiness can be found, even in the darkest of times, if one only remembers to turn on the light.
Albus Dumbledore
Harry Potter and the Prisoner of Azkaban movie
There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.
-- Albert Einstein
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25 Feb 2008 22:59:07 IST
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1st is right
secod is wrong
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" Always remember money isn't everything but make sure you have made a lot of it before talking such nonsense!"
- Bill Gates |
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25 Feb 2008 23:01:28 IST
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wat's the mistake????????????
pls tell.....
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LOKESH SARDANA,
department of Production and Industrial engineering,
Indian Institute of Technology,Roorkee.
Happiness can be found, even in the darkest of times, if one only remembers to turn on the light.
Albus Dumbledore
Harry Potter and the Prisoner of Azkaban movie
There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.
-- Albert Einstein
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25 Feb 2008 23:07:14 IST
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no of ways in which 3 are wrong
=4*2*1=8 ways
no of ways in which 2 are wrong
= 4C2*1
=6 ways
no of ways in which all 4 are wrong
=9
so total=23
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" Always remember money isn't everything but make sure you have made a lot of it before talking such nonsense!"
- Bill Gates |
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25 Feb 2008 23:09:42 IST
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Is the answer 32 ????
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My birthday is no ordinary day.
Its the day when i declared in my own voice,
I WILL NOT GO QUIETLY INTO THE NIGHT,
I WILL NOT VANISH WITHOUT A FIGHT,
I AM GOING TO LIVE ON,
I AM GOING TO SURVIVE,
I AM GOING TO GET WHATEVER I WANT.
I CELEBRATE MY BIRTHDAY, AS MY INDEPENDENCE DAY !!!!!!!!! |
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25 Feb 2008 23:16:34 IST
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how u got 32 akhil bhai???????
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25 Feb 2008 23:18:31 IST
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i got 23 yaar
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" Always remember money isn't everything but make sure you have made a lot of it before talking such nonsense!"
- Bill Gates |
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25 Feb 2008 23:19:35 IST
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@ akhil
pls xplain in detail.....
i m unable to catch ur method
spl first 2 cases....
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LOKESH SARDANA,
department of Production and Industrial engineering,
Indian Institute of Technology,Roorkee.
Happiness can be found, even in the darkest of times, if one only remembers to turn on the light.
Albus Dumbledore
Harry Potter and the Prisoner of Azkaban movie
There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.
-- Albert Einstein
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ok for no of ways in which 3 are wrong...
fix 1 letter to be right...
3 letters and 3 envelopes left...
first one can go in 2 out of these 3 letters(1 is correct...we dont want that)
2 remain...obviously 1 is rigth and 1 is wrong...so only one choice
so that means 1*2=2 cases per right letter
but then we can choose first letter in 4 ways
hence total ways=2*4=8....(1)
for n=2
fix 2 right...done in 4C2 ways..
now obviously we hv 2 letters and 2 envelopes...to go in wrong envelope each has only one choice
so total=4c2*1=4c2=6 ways
all 4 wrong...9 is quite obvious
so total=23
hope u get it
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" Always remember money isn't everything but make sure you have made a lot of it before talking such nonsense!"
- Bill Gates |
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25 Feb 2008 23:41:23 IST
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got it !!!!!!!!!
thanx mate.........
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LOKESH SARDANA,
department of Production and Industrial engineering,
Indian Institute of Technology,Roorkee.
Happiness can be found, even in the darkest of times, if one only remembers to turn on the light.
Albus Dumbledore
Harry Potter and the Prisoner of Azkaban movie
There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.
-- Albert Einstein
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26 Feb 2008 08:55:10 IST
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thats simple total no of ways =24 and single cannot be misplaced it can only happen in pairs of 2or more so ans is 24-1(for correct per.)=23
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those who dont believe in god closes the gates of miracles in their life |
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