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02 Nov 2020, 07:30
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E
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Difficulty:
35%
(medium)
Question Stats:
60% (00:49) correct
40%
(01:02)
wrong
based on 86
sessions
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Three unbiased coins are tossed. What is the probability of getting at most two heads?
(A) 1/4
(B) 3/8
(C) 1/2
(D) 3/4
(E) 7/8
(A) 1/4
(B) 3/8
(C) 1/2
(D) 3/4
(E) 7/8
02 Nov 2020, 08:12
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Bunuel
Three unbiased coins are tossed. What is the probability of getting at most two heads?
(A) 1/4
(B) 3/8
(C) 1/2
(D) 3/4
(E) 7/8
(A) 1/4
(B) 3/8
(C) 1/2
(D) 3/4
(E) 7/8
at most 2 heads ; ( 0,1,2) possible
total ways 1/8
no head ; TTT 1
1 head ; TTH ; 3!/2! ; 3
2 head ; THH ; 3!/2! ; 3
total possiblities of at most 2 heads ; 1+3+3 ; 7
P ; 7/8
option E
02 Nov 2020, 08:53
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The phrase 'getting most two heads' sounds tricky and confusing, so I interpret it as 'not getting three heads.'
Getting most two heads means I can get 0 heads, 1 heads, or 2 heads. But not three heads.
The probability for getting 3 heads on three tosses: 1/2x1/2x1/2=1/8
the probably for not getting 3 heads: 1-(1/8)=7/8
E
Getting most two heads means I can get 0 heads, 1 heads, or 2 heads. But not three heads.
The probability for getting 3 heads on three tosses: 1/2x1/2x1/2=1/8
the probably for not getting 3 heads: 1-(1/8)=7/8
E
