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![[Post New]](/templates/default/images/icon_minipost_new.gif) 24 Mar 2008 19:22:35 IST
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7 digits from numbers 1,2,3,4,5,6,7,8,9 are written in random order find that the 7 digit number is divisible by 9
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24 Mar 2008 19:26:02 IST
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since the sum of all these 9 nos is divisivle by 9,
to obtain suitable pairs we simply have to remove all 2-number papers that add up to 9
so we remove (1,8),(2,7),(3,6),(4,5)
hence 4 pairs of numbers are obtained...in which all permutations are divisible by 9
each no can be arranged in 7! ways
so no of such nos= 4*7!
total no of ways of selecting and permuting 7 nos=9P7
so
Prob= 4*7!/9P7
=1/9
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