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WAEC Mathematics 2021 Paper

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Question : 45

Total: 49

A box contains 40 identical balls of which 10 are red and 12 are blue. if a ball is selected at random from the box what is the probability that it is neither red nor blue?

$\;\frac{9}{20}$
$\;\frac{3}{10}$
$\;\frac{1}{4}$
$\;\frac{11}{20}$

Solution:

Concept:

Probability of an event is the favourable number of outcomes divided by the total number of outcomes.

Explanation:

Total balls

= 40

.

Red balls

= 10

, so

P(\text{red}) = \frac{10}{40}

.

Blue balls

= 12

, so

P(\text{blue}) = \frac{12}{40}

.

The event "neither red nor blue" is the complement of "red or blue".

Thus,

P(\text{neither red nor blue}) = 1 - \frac{10}{40} - \frac{12}{40}

.

= \frac{40 - 10 - 12}{40} = \frac{18}{40} = \frac{9}{20}

.

Answer:

\frac{9}{20}

Option A.

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