Answer:
0.3667 or 36.67%
Step-by-step explanation:
The probability of getting at least 1 defective hard disk among the 5 (P(X>0)) is equal to 100% minus the probability of getting none defectives (1-P(X=0)).
If 23 out of 25 hard disks are non-defective, the probability is:

The probability that there is at least 1 defective hard disk is 0.3667 or 36.67%.
Probability that one is hired ans one not:
P ( A ) = (2 C 1 * 4 C 4) / 6 C 5 =
= ( 2 * 1 ) / 6 = 2/9 = 1 / 3
Answer: 1/3 or 33.33%
It is not too difficult. Just do this
50-15
5(10-3)
The answer is 5(10-3)
D/H = 0.25
18/H = 0.25/1
Cross multiply and solve for H