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JAMB Mathematics 2017 Paper

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Question : 3

Total: 44

If U = {x : x is an integer and 1 ≤ x ≤ 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

$\frac{3}{4}$
$\frac{3}{10}$
$\frac{1}{4}$
$\frac{1}{20}$

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}

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