Final answer:
The probability of selecting 5 out of 7 defective phones is approximately 0.3263.
Step-by-step explanation:
To find the probability that 5 out of 7 randomly selected phones are defective, we need to use the concept of hyper-geometric distribution.
The probability of selecting 5 defective phones out of 7 is given by:
P(5 defective phones) = (C(8,5) * C(5,2)) / C(13,7)
where C(n,r) represents the combination of n items taken r at a time.
By evaluating the expression, we find that:
P(5 defective phones) = (56 * 10) / 1716
= 0.3263
Therefore, the probability that 5 of the 7 randomly selected phones are defective is approximately 0.3263, rounded to four decimal places.