Probability Question (1 Viewer)

[smithjohn]

Please show working.

 

[pikachu975]

P(at most 2 heads) = P(0 heads) + P(1 head) + P(2 heads)
= P(3 tails) + P(2 tails) + P(1 tail)
= 36/100 + 29/100 + 20/100
= 17/20 (not an option)

But I think the question has a typo because it says "counting the number of heads" is the experiment and the table has "number of tails". I think it's meant to have "number of heads" which then becomes:
P(at most 2 heads) = P(0 or 1 or 2 heads)
= 15/100 + 20/100 + 29/100
= 16/25 (B)

 

[tickboom]

You may find this video explanation helpful, where I show a few alternative ways to think about this one. Enjoy!