<PRE><B>Question 1112565</B>
use the binomial distribution
:
Probability ( P ) ( k successes in n trials ) = nCk * p^k * p^(n-k), where nCk = n! / (k! * (n-k)!)
:
for this problem, n=7, k=1, p = 1-0.20 = 0.80 (the probability of being late)
:
P ( 1 failure in 7 sent for delivery parcels ) = 7C1 * (0.80)^1 * (1-0.80)^(7-1)
:
P ( 1 failure in 7 sent for delivery parcels ) = 0.00036 
:
</PRE>