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2025 WAEC Mathematics Theory a. A box contains 5 blue balls, 3 black balls, and 2 red balls of...

Mathematics
WAEC 2025

a. A box contains 5 blue balls, 3 black balls, and 2 red balls of the same size. A ball is selected at random from the box and then replaced. A second ball is then selected. Find the probability of obtaining: two red balls

b. A box contains 5 blue balls, 3 black balls, and 2 red balls of the same size. A ball is selected at random from the box and then replaced. A second ball is then selected. Find the probability of obtaining: two blue balls or two black balls

c. A box contains 5 blue balls, 3 black balls, and 2 red balls of the same size. A ball is selected at random from the box and then replaced. A second ball is then selected. Find the probability of obtaining: one black ball and one red ball in any order

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Explanation

a. Total ball = 5 blues + 3 blacks + 2 red balls = 10 balls

Selection with replacement

Pr(1st red ball) = \(\frac{2}{10}\)

Pr(2nd red ball) = \(\frac{2}{10}\)

Therefore, Pr(two red balls) =  \(\frac{2}{10}\) x  \(\frac{2}{10}\) = \(\frac{4}{100}\)

=  \(\frac{1}{25}\) = 0.04

b. Pr( of selecting 2 blue) =  \(\frac{5}{10}\) x  \(\frac{5}{10}\) =  \(\frac{25}{100}\)

                                        =  \(\frac{1}{4}\)

Pr(of selecting 2 black balls) =  \(\frac{3}{10}\) x  \(\frac{3}{10}\) =  \(\frac{9}{100}\)

Pr( 2 blue or 2 black balls) =  \(\frac{1}{4}\) +  \(\frac{9}{100}\) =  \(\frac{25}{100}\) +  \(\frac{9}{100}\) =  \(\frac{34}{100}\) = 0.34.

c) 1 black, and 1 red in any other means it can be 1 black, and 1 red, and 1 black

=  \(\frac{3}{10}\) x  \(\frac{2}{10}\) +  \(\frac{2}{10}\) +  \(\frac{3}{10}\)

 =  \(\frac{6}{100}\) +  \(\frac{6}{100}\) =  \(\frac{12}{100}\) = 0.12.


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