Answer:
0.07047
Step-by-step explanation:
at least 4 people survive is
4 people survive and 2 don't +
5 people survive and 1 doesn't +
all 6 people survive
the probability of 4 people to survive is the product of the individual probabilities :
0.3×0.3×0.3×0.3 = 0.3⁴ = 0.0081
times the probability 2 don't survive
0.7×0.7 = 0.49
0.0081×0.49 = 0.003969
now, the chance that 4 out of 6 survive is that probabilty times how many times we can select 4 out of 6.
to select 4 out of 6 is
[tex] \binom{6}{4} [/tex]
= 6! / (4! × (6-4)!) = 6! / (4! × 2!) = 6×5/2 = 30/2 = 15
so, the probability of having 4 survivors is
15×0.003969 = 0.059535
the probability of 5 people surviving is 0.3⁵ times one not
0.3⁵×0.7 = 0.001701
we have 6 over 5 combinations to pick 5 out of 6 = 6.
so, in total for 5 survivors we get
6×0.001701 = 0.010206
and the probabilty of all 6 surviving is
0.3⁶ = 0.000729
so, the probability of at least 4 out of 6 surviving is
0.059535 +
0.010206 +
0.000729
---------------
0.070470
