# contest R2 Q12

When flipping an unbiased cin determine the probability that

i> at least three trials are necessary to observe a head

ii> at most three trials are necessary to observe a head

iii> the first head occurs on the third trial Forward This Problem to Friend

When flipping an unbiased cin determine the probability that
i> at least three trials are necessary to observe a head
ii> at most three trials are necessary to observe a head
iii> the first head occurs on the third trial

jnvmahesh@gmail.comSubscriberSOLVE - ΜΔΓΗŠ
i>

1)1/8

2)7/8

3)1/8

its required 2 flips to see head in unbiased coin so

2>at most three trials are necessary (2<3)

Answer

i> 1/4=0.25

ii> 7/8=0.875

iii> 1/8=0.125

1/8

1/4, 7/8 and 1/8