Total no of balls = 30 Let x = no. of red balls Pr(red) = \(\frac{x}{30}\) Pr(black) = \(\frac{3}{10} = \frac{9}{30}\) Pr(white) = \(\frac{2}{5} = \frac{12}{30}\) No. of black balls = 9 No. of white balls = 12 9 = 12 + x = 30 x = 30 - 21 x = 9 No. of red balls = 9

A box contains black, white and red identical balls. The probability of picking a black ball at random from the box is \(\frac{3}{10}\) and the probability of picking a white ball at random is \(\frac{2}{5}\). If there are 30 balls in the box, how many of them are red?

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