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  1. Chapter 15 Class 10 Probability
  2. Serial order wise
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Ex 15.2, 3 A bag contains 5 red balls and some blue balls. If the probability of drawing a blue ball is double that of a red ball, determine the number of blue balls in the bag.The bag contains red and blue balls. Number of red balls = 5 Let Number of blue balls = x ∴ Total number of balls = 5 + x Given, Probability of drawing a blue ball is double that of a red ball. Probability of drawing blue ball = 2 × Probability of drawing red ball Probability = (𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑙𝑢𝑒 𝑏𝑎𝑙𝑙𝑠)/(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑎𝑙𝑙𝑠) = 𝑥/(5 + 𝑥) Probability = (𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑟𝑒𝑑 𝑏𝑎𝑙𝑙𝑠)/(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑎𝑙𝑙𝑠) = 5/(5 + 𝑥) Probability of drawing blue ball = 2 x Probability of drawing red ball 𝑥/(5 + 𝑥) = 2 × 5/(5 + 𝑥) 𝑥 = 2 × 5 𝑥 = 10 ∴ There are 10 blue balls in the bag.

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Davneet Singh
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.