Q. A number $n$ is chosen at random from the set {11, 12, 13, ……, 30}. The probability that $n$ is neither divisible by 3 nor divisible by 5 is
A) $\frac{7}{20}$
B) $\frac{9}{20}$
C) $\frac{11}{20}$
D) $\frac{13}{20}$
Explanation
(c)
Number which are divisible by either 3 or 5 are 12,15,18,20,21,24,25,27,30
Total number=9
$P($number either divisible by 3 or 5)$= \frac{9}{20}$
$P($number neither divisible by 3 nor 5)
$= 1 - P($either divisible by 3 or5)
$= 1 - \frac{9}{20} = \frac{11}{20}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.