Permutations good ones

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1)In a certain test, there are n questions .In the test 2^n-1 students gave wrong answers to atleast i questions, where i=1,2,3,....n. If the total number of wrong answers given is 2047, then find the value of n.
2)A person goes in an examination where there are four papers of m marks each. The number of ways in which he can get 2m marks is?
3)A student is to answer 10 questions out of 10 in an exam such that he must choose atleast 4 from the first five questions. The number of choices available is ?(seems obv but i cant und the answer given)
answers quickly pls...

#Mathematics #Algebra

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38 Answers

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1

Thedarkknight ·2009-01-22 09:58:06

@ integrations
wow exactly.......
can ya pls explain it?

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Lokesh Verma ·2009-01-22 09:58:37

and in question 1 i am almost sure that the power should be n-i

otherwise that question is a stupid one..

it means that n. 2 ^n-1 = 2047 which will have no integer solution...

Otherwise it will have an answer...

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Â°áƒ¦â€¢à¹“ÑÏ…Î ·2009-01-22 09:58:52

2^(n)-1=2047
2^n=2048
thus n=11

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Thedarkknight ·2009-01-22 10:00:08

sir but integrations seems to have got the correct answer ......i am waiting for her expln...

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Thedarkknight ·2009-01-22 10:02:20

cool....but then why all othr details wit i an all have been given?

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Lokesh Verma ·2009-01-22 10:02:42

Even i am waiting for integrations' explanation... I dont think the expression she wrote makes sense!

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Lokesh Verma ·2009-01-22 10:04:19

you should use

Î£ i.2^n+1-i = 2047

where limit is from 1 to n

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Asish Mahapatra ·2009-01-22 10:04:45

the 1 should be i in the question otherwise it cant be solved.

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Your Answer

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