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February 21, 2018, 05:10:55 PM
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: Which side faces up?  ( 3020 )
« : May 29, 2007, 11:07:03 PM From Poonam»

Which side faces up?

There are 10 coins kept on a table in a room. All are heads initially.

1. One coin is picked up RANDOMLY and turned.(Head to tail or Tail to head).
2. The step 1 is repeated randomly 51 times.
3. One coin is covered.
4. You are called in the room and told what has happened till now
5. You see, out of nine uncovered coins 5 coins are Heads, 4 coins are tails.

Which side faces up in the covered coin?

PS: It appeared in CAT 1999.

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« #1 : May 29, 2007, 11:28:12 PM From PSM»

total time the process took place is 52
its heads....because .......
5 coins are heads...  so no. of time they have been turned is even.......
and the other 4 tail coins have been turned odd no. of times let them be a1,a2,a3,a4........now a1+a2+a3+a4 is even because all r odd..........
sum of the turns of head coins is also even .....even +even makes it even.and 52 is even...........so the last coin was also turned up even times thats why the answer is heads...........

if anything wrong please reply...
« #2 : May 30, 2007, 11:19:00 PM From Prateek»

PSM has read the question wrong!

The covered coin faces tail up, since the coin is tossed 51 times.
« #3 : May 31, 2007, 12:56:08 AM From PSM»

might be thats why i specified that the step is being processed 52 times.....
n my answer was heads but because as u say it is 51 then answer is tails....
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