If U = {x : x is an integer and 1 \le x \le 20 }
E1 = {x: x is a multiple of 3}
E2 = {x: x is a multiple of 4} and an integer is picked at random from U, find the probability that it is not in E2
A
\(\frac{3}{4}\)
B
\(\frac{3}{10}\)
C
\(\frac{1}{4}\)
D
\(\frac{1}{20}\)
Verified Correct Answer: A.
Step-by-Step Mathematical Solution
U = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}
E1 = {3, 6, 9, 12, 15, 18}
E2 = {4, 8, 12, 16, 20}
Probability of E2 = \(\frac{5}{20}\) i.e \(\frac{\text{Total number in}E_2}{\text{Entire number in set}}\)
Probability of set E2 = 1 − \(\frac{5}{20}\)
= \(\frac{15}{20}\)
= \(\frac{3}{4}\)
Source: Myschool Past Questions Archive (Record #46323)