Question

A box contains cards numbered from 1 to 20. A card is drawn at random. Find the probability that the card drawn bears:
i) a prime number
ii) an even number
iii) a number divisible by 4
iv) a factor of 20
[4 MARKS]

Answer 1

Each subpart: 1 Mark each

i) Prime numbers from 1 to 20 are 2, 3, 5, 7, 11, 13, 17 and 19
$\therefore$ P(a prime number) $=\frac{8}{20}=\frac{2}{5}$

ii) P(an even number) $=\frac{10}{20}=\frac{1}{2}$

iii) 4, 8, 12, 16 and 20 from the given numbers are divisible by 4
$\therefore$ P(a number divisible by 4) $=\frac{5}{20}=\frac{1}{4}$

iv) 1, 2, 4, 5, 10 and 20 are the factors of 20
P(a factor of 20) $=\frac{6}{20}=\frac{3}{10}$