Answer:
0.9885 (98.85%)
Step-by-step explanation:
Since sample is less than 10% of the population, we can use binomial distribution to approximate the probability.
So we want to calculate P( X < 20 ).
We can calculate the probability of complement event P( X = 20 ).
Use binomial formula b(x; n, p) = C( n, x ) p^(x) (1-p)^(n-x)
b( 20; 20, 0.8 )
= C( 20, 20 ) (0.8)^(20) (0.2)^0
= (0.8)^20 ≈ 0.0115
So since P( X < 20 ) = 1 - P( X = 20 ), we have
P( X < 20 ) ≈ 1 - 0.0115 = 0.9885
