in a certain test there are n ques. . in the test 2n-i gave the wrong answers to atleast i ques...... whr i = 1,2,.......n . if the total number of wrong answers given is 2047,then n= ?
answer is n=11............ see, in the test 2^n-i students gave the answers to atleast i questions incorrectly.........hence the no. of students who exactly gave the answers i questions incorrectly=2^n-i -2^n-(i+1) therefore the students who answered all the questions incorrectly will be 2^0=1 hence for i=1,2,3.........n 1(2^n-1 - 2^n-2) + 2(2^n-2 - 2^n-3) +.............................+n(2^0)=2047 or 2^n-1 + 2^n-2 + ...............................+n=2047 2^n - 1=2047 2^n = 2048 or n=11 cheers!!!!!
Moderation Team
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[i=n] 2n-i 
