NCERT Solutions for Class 10 Maths Chapter 15

Important NCERT Questions

PROBABILITY

NCERT Books for Session 2022-2023

CBSE Board and UP Board Others state Board

EXERCISE 15.2

Page No:311

Questions No: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.

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Let the number of blue balls be x.

Number of red balls = 5

Total number of balls = x + 5

P (getting a red all) = 5/(5 + x)

P (getting a blue ball) = x/(5 + x)

Given that,

2(5/(5 + x)) = (x/(5 + x)) ⇒ 10(x + 5) = x² + 5x – 50 = 0

⇒ x² – 10x + 5x – 50 = 0 ⇒ x(x – 10) + 5(x – 10) = 0

⇒ (x – 10)(x + 5) = 0

⇒ Either x – 10 = 0 or x + 5 = 0

⇒ x – 10 or x = -5

However, the number of balls cannot be negative.

Hence, number of blue balls = 10