Question 12 - CBSE Sample Paper Class 10 - 2017-18

Last updated at May 29, 2018 by Teachoo

A box contains 12 balls of which some are red in colour. If 6 more red balls are put in the box and a ball is drawn at random, the probability of drawing a red ball doubles than what it was before. Find the number of red balls in the bag.

Question 12A box contains 12 balls of which some are red in colour. If 6 more red balls are put in the box and a ball is drawn at random, the probability of drawing a red ball doubles than what it was before. Find the number of red balls in the bag.Given,
Total balls in the box = 12
Red balls in the box = x
Probability of drawing a red ball = (๐๐ข๐๐๐๐ ๐๐ ๐๐๐ ๐๐๐๐๐ )/(๐๐๐ก๐๐ ๐๐ข๐๐๐๐ ๐๐ ๐๐๐๐๐ )
= ๐ฅ/12
If 6 more red balls are put in the box,
Total number of balls = 12 + 6 = 18
Number of red balls = x + 6
Probability of drawing a red balls = (๐ฅ + 6)/18
Given, after adding 6 balls, probability of drawing a red ball is
double of what it was before.
โด New Probability = 2 ร Old probability
(๐ฅ + 6)/18 = 2 ร ๐ฅ/12
(๐ฅ + 6)/18 = ๐ฅ/6
6 [(๐ฅ + 6)/18] = ๐ฅ
(๐ฅ + 6)/3 = ๐ฅ
๐ฅ+6 = 3๐ฅ
6 = 3๐ฅโ๐ฅ
6 = 2๐ฅ
2๐ฅ = 6
๐ฅ" = " 6/2
๐ฅ = 3
โด Number of red balls = x = 3

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.