Question

a box contains 3 black balls , 7 white balls and 5 red balls . one ball is lost . the probability that a red ball is drawn is 2/7 . The colour of the lost ball is

Answer 1

Of the 15 balls, 14 remain.
P(red) = 2/7 means there are 4 red balls out of 14.
So, the lost ball is red.