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NCERT Solutions Class 10 Mathematics Solutions for Probability - Exercise 15.1 in Chapter 15 - Probability

Question 25 Probability - Exercise 15.1

A box contains 12 balls out of which x are black. If 6 more black balls are put in the box, the probability of drawing a black ball is now double of what it was before. Find x

Answer:

Total number of black balls = x

Total number of balls = 12

P(E) = (Number of favourable outcomes/ Total number of outcomes)

P (getting black balls) = x/12 ——————-(i)

Now, when 6 more black balls are added,

Total balls become = 18

∴ Total number of black balls = x+6

Now, P (getting black balls) = (x+6)/18 ——————-(ii)

It’s given that, the probability of drawing a black ball now is double of what it was before

(ii) = 2 × (i)

(x+6)/18 = 2 × (x/12)

x + 6 = 3x

2x = 6

∴ x = 3

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