MA Economics Entrance Coaching › Forums › Subject forums › Math › permutation and combination
Tagged: engineering module
This topic contains 5 replies, has 3 voices, and was last updated by rohit pandey 4 years, 9 months ago.

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August 11, 2014 at 12:15 pm #525
q1 a seven digit no divisible by 9 is to be formed by using 7 no’s out of {1,2,3,4,5,6,7,8,9} the no of ways in which this can be done is? final ans:4*7!
q2 the no f ways in which 3 girls and 3 boys all of diff heights be arranged in a line so tht the boys as well as girls among themselves are arranged in decreasing order of their heights(frm left to right)?
final ans:20
shruti290Quote 
August 12, 2014 at 7:52 am #542
shruti the answer for q2 is indeed 20 but i will have to explain it in class.hint try forming a tree its really big.
and for q1 if you take and sum the different permutations of 7 numbers form set you will find the sum of 4 options is divisible by 9 hence 4*7!.
rohit pandeyQuote 
August 13, 2014 at 12:56 pm #554
this is if first choice is g1 which has ten ways now for b1 also there willbe 10 ways.
rohit pandeyQuote 
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