probability question.

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Junior | Next Rank: 30 Posts
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by mtg123 » Wed Oct 03, 2007 1:37 pm
Total number of ways of selecting 1 from junior and 1 from senior =
1000 C 1 * 800 C 1 = 1000 * 800

As there are 60 sibling PAIRS,
Number of ways of selecting 1 from junior and 1 from senior so that they are Sibling pair = 60 C 1 * 60 C 1 = 60 * 60

Required probality = Number of favorable events / total number of events
= (60 * 60 ) / (1000 * 800 )
= 9 / 2000


Please let me know the OA
Source: — Problem Solving |

Junior | Next Rank: 30 Posts
Posts: 22
Joined: Fri Aug 31, 2007 8:14 am

by mtg123 » Wed Oct 03, 2007 1:37 pm
Total number of ways of selecting 1 from junior and 1 from senior =
1000 C 1 * 800 C 1 = 1000 * 800

As there are 60 sibling PAIRS,
Number of ways of selecting 1 from junior and 1 from senior so that they are Sibling pair = 60 C 1 * 60 C 1 = 60 * 60

Required probality = Number of favorable events / total number of events
= (60 * 60 ) / (1000 * 800 )
= 9 / 2000


Please let me know the OA