NDA Math Probability

Probability of hitting the forget =0.3
If’n' is the no. of times that the Missile is fired
∴ Probability of hitting at least once=1−[1−0.3]n=0.8
0.7n=0.2
n‌log‌0.7=log‌0.2
⇒n=4.512
for n=4;=p<0.8
take n=5
n=5
Hence 5 missiles should be fired so that there is at least 80% prob. that the target is hit.