Comprehension In a bag, there are 17 red balls, some green, and some blue balls. The probability of drawing a green ball is (1/7)th more than that of

Question

Find the number of blue balls in the bag.
1. 27
2. 26
3. 20
4. none of these
5. cannot be determined

Answer 1

Correct Answer - Option 3 : 20

Calculation:

Let the number of green balls and blue balls present in the bag be 'g' and 'b' respectively

Also, number of red balls = 17

Total number of balls = (17 + g + b)

Probability of drawing a red ball = 17/(17 + g + b)

Probability of drawing a green ball = g/(17 + g + b)

Probability of drawing a blue ball = b/(17 + g + b)

Now a/q we have

⇒ g/(17 + g + b) = 1/7 + 17/(17 + g + b)

⇒ (g - 17)/(17 + g + b) = 1/7 

⇒ 6g - b = 136    .....(i)

also, 

⇒ b/(17 + g + b) = 1/21 + 17/(17 + g + b) 

⇒ (b - 17)/(17 + g + b) = 1/21

⇒ 20b - g = 374    .....(ii)    

using equation (i) and (ii), we get 

g = 26, b = 20

∴ Required number of blue balls = 20