Explanation:
Probability is the ratio of the expected outcome (event) to the total outcome (sample space)
Probability = expected outcome/total outcome
If Playing cards numbered from 1 to 20 are mixed thoroughly and kept it in a box, the total number of sample space is 20
1) To calculate of getting a prima number.
Events = {2, 3, 5, 7,11,13,17,19}
n(events) = 8 elements
Pr(selecting a prime) = 8/20 = 2/5
2) If a factor of 20 is selected
Factor of 20 F = {2, 4, 5, 10, 20}
n(F) = 5
Pr(factor of 20) = 5/20 = 1/4
3) A composite number are 2 digits numbers.
Composite number C = {10,11,12,13,14,15,16,17,18,19,20}
n(C) = 11
Pr(a composite number) = 11/20
4) For multiple of 3.5
Multiple of 3.5 M = {3.5, 7.0, 10.5, 14.0, 17.5}
n(M) = 5
Pr(multiple of 3.5) = 5/20 = 1/4
5) For perfect squares
Perfect squares P = {1, 4, 9, 16}
n(P) = 4
Pr(perfect squares) = 4/20 = 1/5