Coins/Probabilty

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venmic: Master | Next Rank: 500 Posts; Posts: 222; Joined: Mon Oct 13, 2008 4:04 pmFollowed by: 2 members; Thanked: 3 times

by venmic » Tue May 10, 2011 8:00 pm

If 5 fair coins are tossed, how many different coin sequences will have exactly 3 tails, if all tails have to occur in a
row?

Please suggest

Thankx

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Source: Beat The GMAT — Problem Solving | Tue May 10, 2011 8:00 pm

manpsingh87: Master | Next Rank: 500 Posts; Posts: 436; Joined: Tue Feb 08, 2011 3:07 amFollowed by: 6 members; Thanked: 72 times

by manpsingh87 » Tue May 10, 2011 10:16 pm

venmic wrote:If 5 fair coins are tossed, how many different coin sequences will have exactly 3 tails, if all tails have to occur in a
row?

Please suggest

Thankx

{TTT}HH; since all tails have to occur in row so consider them as a one group, therefore in all we have, 3 elements to arrange, {TTT},H,H; which can arrange themselves in 3!/2!=3

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