Question

a box contains 5 green balls and some white balls if the probability of drawing a white ball is half of the probability of drawing green both then find number of white balls in the box

Answer 1

Let the number of white balls in the box = x
then, total number of balls in the box = (5 + x)

so, probability of drawing a white ball = x/(5 + x)
probability of drawing a green ball = 5/(5 + x)

A/C to question,

probability of drawing a green ball = 1/2 × probability of drawing a white ball

5/(5 + x) = 1/2 × x/(5 + x)

x = 10,
hence, number of white ball in the box = 10

[ note :- you did mistake in question, if probability of white ball is half the probability of green ball them, number of white ball is 5/2. which is not integer. definitely question should be probability of green ball is half of probability is white ball ]