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WAEC Mathematics 2020 Paper

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Question : 37

Total: 48

A box contains 12 identical balls of which 5 are red, 4 blue, and the rest are green. If two balls are selected at random one after the other with replacement, what is the probability that both are red?

$\;\frac{25}{144}$
$\;\frac{5}{33}$
$\;\frac{5}{6}$
$\;\frac{103}{132}$

Solution:

Concept:

Probability of independent events with replacement is found by multiplying the individual probabilities.

Explanation:

Total balls

= 12

.

Number of red balls

= 5

.

So,

P(\text{red}) = \frac{5}{12}

.

Since the ball is replaced, the second draw has the same probability.

Therefore,

P(\text{both red}) = \frac{5}{12} \times \frac{5}{12} = \frac{25}{144}

.

Answer:

\frac{25}{144}

Option A.

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