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Probability of atleast 3 heads

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by DanaJ » Sat Apr 04, 2009 3:59 am
I'd go with 5/32 and here's my reasoning:
There are favorable and unfavorable cases to each of the five tosses, and since each case has a probability of 1/2, you'll always have a total probability of 1/2*1/2*1/2*1/2*1/2 = 1/32 for your event. The distribution is as follows:

H H H T T

T H H H T

T T H H H

T H H H H

H H H H T

H H H H H

Since each of the cases above is obtained by having a suite of 5 favorable tosses, then the total probability will be 5*1/32 = 5/32.
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by Vemuri » Sat Apr 04, 2009 10:46 pm
DanaJ wrote:I'd go with 5/32 and here's my reasoning:
There are favorable and unfavorable cases to each of the five tosses, and since each case has a probability of 1/2, you'll always have a total probability of 1/2*1/2*1/2*1/2*1/2 = 1/32 for your event. The distribution is as follows:

H H H T T

T H H H T

T T H H H

T H H H H

H H H H T

H H H H H

Since each of the cases above is obtained by having a suite of 5 favorable tosses, then the total probability will be 5*1/32 = 5/32.
DanaJ, you did a calculation error. The number of favorable cases as per your explanation is 6 not 5.
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by cramya » Sat Apr 04, 2009 10:55 pm
I would go with A

3 heads or 4 heads or 5 heads

Pick 5 spots there are three ways to get 3 heads 9in consecutive tosses and 2 tails

1/32+1/32+1/32 = 3/32

For 4 consecutive heads there are 2 ways to get it in 5 tosses

2/32

5 consecutive heads there is only one choice = 1/32

3/32+2/32+1/32
= 6/32
= 3/16
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by piyush_nitt » Sat Apr 04, 2009 11:14 pm
cramya wrote:I would go with A

3 heads or 4 heads or 5 heads

Pick 5 spots there are three ways to get 3 heads 9in consecutive tosses and 2 tails

1/32+1/32+1/32 = 3/32

For 4 consecutive heads there are 2 ways to get it in 5 tosses

2/32

5 consecutive heads there is only one choice = 1/32

3/32+2/32+1/32
= 6/32
= 3/16
IMO B

HHHTT
TTHHH
THHHT

HHHHT
THHHH
HTHHH
HHHTH

HHHHH

= 8/32
= 1/4

OA pls?
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by cramya » Sat Apr 04, 2009 11:20 pm
Piyush,

HTHHH
HHHTH

These wont be consecutive tosses, correct?

Regards,
CR
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by piyush_nitt » Sat Apr 04, 2009 11:29 pm
cramya wrote:Piyush,

HTHHH
HHHTH

These wont be consecutive tosses, correct?

Regards,
CR
Yes Cramya! Right!

But above represents a scenario of 3 consecutives tosses, correct?
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by cramya » Sun Apr 05, 2009 12:30 am
Piyush,
I think u could be right on that...

Regards,
Cramya
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by Vemuri » Sun Apr 05, 2009 1:46 am
OA is B
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