Question

1.
There are 12 identical balls of different colours in a bag. If 6 more black balls are
added then probability of drawing black balls increases by 1
12.
Find the original number of black balls.​

Answer 1

Answer:

by 12 because the black ball will look different in many different colour of ball s

Answer 2

Given :-

Total balls in the bag = 12

Let the number of black balls be x .

∴ Probability of drawing a black ball

                              $= \frac{\sf{Number \ of \ black \ balls }}{\sf{Total \ number \ of \ balls}}\\\\= \frac{\bold{x}}{\bold{12}}$

If 6 more black balls are   added ,

Total number of balls = 12 + 6 = 18  

⇒ Number of black balls = x + 6

∴ Probability of drawing a black balls = $\sf{\frac{x+6}{18}}$

Given , after adding 6 more black balls , probability of drawing a black ball increases by  ¹/₁₂

∴ New probability = Old Probability + ¹/₁₂

$\sf{\frac{x+6}{18} = \frac{1}{12} + \frac{x}{12} }\\\\\implies\sf{\frac{x+6}{18} = \frac{x+1}{12}}$

⇒ 12 ( x +  6 ) = 18 ( x + 1 )

⇒ 12x + 72 = 18x + 18

⇒ 18x - 12x = 72 - 18

⇒ 6x = 54

⇒ x = 9

∴ The original number of black balls was 9 .