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Ask iit jee aieee pet cbse icse state board experts Discussion Response Post to: Permutation & combinations ( ARIHANT ALGEBRA ) page no 426 <q no 8>
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rhd92781 (686)

Blazing goIITian

Olaaa!! Perrrfect answer. 118  [166 rates]

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total posts: 526    
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yeah...the ans does cum 828.
1) No of ways to select 2 professors:
Case 1: If P1 is selected, P2 can't be selected. We have to select one more frm 3 professors which can be done in 3C1 ways.
The same of we select P2 and not P1.
Hence total no. of ways = 2*3C1 = 2*3=6

Case 2: If both P1 and P2 aren't selected. Then we have to select 2 prof out of 3.
No of ways = 3C2 = 3
Hence total no. of ways to select professors = 6+3=9.

2) The no of ways to select the students:
Case 1: If S2 is present, we hav to select 2 more students out of 9 (S1 can be selctd).
No. of ways = 9C2.

Case 2: If S2 isn't present, we have to select 3 students out of 8 since S1 also can't be selected.
No. of ways = 8C3.

Total no of ways to select students = 9C2+8C3 = 92

Hence total no. of committees possible = 9*92 = 828.

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I am only one,
But still I am one.
I cannot do everything,
But still I can do something;
And because I cannot do everything
I will not refuse to do the something that I can do.
- Edward Everett Hale
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