There are 30 balls, out of which 60% are green balls and the rest are blue balls. How many ways that we can pick the pair of blue balls?A. 21B. 2C. 12.D. none

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Arun

  • Jul 22nd, 2005
 

21

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parshuram

  • Feb 16th, 2006
 

Answer is 12

60 %  of 30 balls are 18

remaining are 12

So answer is 12

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gaurav

  • Jul 24th, 2006
 

60% r green balls i.e.18......

so 12 r blue........now we can remove PAIR of two balls in 12c2 ways i.e(12*11)/2.......so answer is NONE.

jay

  • Dec 1st, 2006
 

fantastic

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AKSHAYIT

  • Dec 10th, 2006
 

n C r = n ! / ( r ! * ( n - r ) ! )andn P r = n ! / ( n - r ) !and in question order of elements is not important as 2 balls to be selectes have to be of blue colourand therefore we use combinationtherefore ans= 12! / ( 2 ! * 10 ! ) = 12*11*10! / 2*10! = 66 =none

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shafi_521

  • Oct 22nd, 2009
 

60% of 30 i.e., 60(30/100)=18, so we have 18 green balls ans the remaning 12 balls are of blue.
 we can select pair of blue balls from 12 blue balls in 12c2 ways i.e., (12 * 11)/(2 * 1) =66 ways.
so our ans is D.

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