UPSC Maths Problems Challenge : A Problem A Day! (Day 16)

This is the time for another question from Probability! UPSC questions (except those asked in prelims) involve a lot of aptitude based task and these require both logic and mathematical skill in order to be solved.This is a nice question I believe is solvable if you pay attention to the x factor you obviously need in cracking aptitude questions : logic.

Read on to find the solution to the problem.

(Original Photograph Source)

Today's Problem(28/06/2015)

Question Credit : http://www.m4maths.com

A bag contains 20 balls. 8 balls are green, 7 are white and 5 are red. What is the minimum number of balls that must be picked up from the bag blind-folded (without replacing any of it) to be assured of picking atleast one ball of each colour?

There are 8 balls that are green and 7 that are white.Now,if we pick 8 + 7 = 15 balls,there remains a chance that 8/8 are green and 7/7 are white,that is all 15 are green and white.Now,if we pick 15+1 = 16 balls,there cannot be more than 15 balls that are green and white,so we will get at least 1 red ball.So,16 is the answer.