Question

a box contain 12 balls of which some are red in colour.if 6 more red balls are put in the box and a ballis drawn at random,the probability of drawing a red ball doubles than wht before. Find the no. of red ball in the bags.

Answer 1

$let \: there \: be \: x \: no. \: of \: red \: balls \\p(getting \: red \: ball) = \frac{x}{12} \\ when \: 6 \: more \: red \: balls \: are \: added \: we \: will \: get \\ total \: red \: balls = x + 6 \\ total \: no. \: of \: balls = 12 + 6 = 18 \\ now...... \\ p(getting \: red \: ball) = \frac{x + 6}{18} \\ \frac{2x}{12} = \frac{x + 6}{18} \\ \frac{x}{6} = \frac{x + 6}{18} \\ 18x = 6x + 36 \\ 12x = 36 \\ x = 3 \: ........answer$