Some white balls put in a basket containing twe... - JAMB Mathematics 2004 Question
Some white balls put in a basket containing twelve red balls and sixteen black balls. If the probability of picking a white balls from the baskets is 3/7, how many white balls were introduced?
A
12
B
21
C
28
D
32
correct option: b
Number of white balls = x
Number of red balls = 12
Number of black balls = 16
Total number of balls = 28 + x
P(white balls) = 3/7
But P(white balls) \(= \frac{x}{28+x}\\ = \frac{3}{7} = \frac{x}{28+x}\\ 3(28 + x) = 7x\\ 84 + 3x = 7x\\ 7x - 3x = 84\\ 4x = 84\\ x = 21\)
Number of red balls = 12
Number of black balls = 16
Total number of balls = 28 + x
P(white balls) = 3/7
But P(white balls) \(= \frac{x}{28+x}\\ = \frac{3}{7} = \frac{x}{28+x}\\ 3(28 + x) = 7x\\ 84 + 3x = 7x\\ 7x - 3x = 84\\ 4x = 84\\ x = 21\)
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