An urn contains five red balls and nine blue balls. Four balls are drawn at random, without replacement. (a) What is the probability that all four balls are red? (Round your answer to four decimal places.) (b) What is the probability that two of the balls are red and two are blue? (Round your answer to four decimal places.)

Respuesta :

The probability that all four balls are red is 0.0050

The probability that two of the balls are red and two are blues is 0.0360

5 Red Balls and 9 Blue Balls

= Four Balls are drawn at random, without replacement

= Total Number of Balls = 5+9=14

The probability that all four balls are red =

P (all four balls are red) = ⁵C₄/¹⁴C₄

Therefore, By nCr = n! / r! (n-r)!

⁵C₄ = 5!/ 4!×(5-4)! = 5

¹⁴C₄ = 14!/ 4!×(14-4)! = 1001

P(All are red) = 5/1001 = 0.00495 = 0.005

Hence the probability that all four balls are red is 0.0050

P (Two balls are red and two balls are blue) = ⁵C₂ ×⁹C₂ / ¹⁴C₄

⁵C₂ = 5!/ 2!×(5-2)! = 10

⁹C₂ = 9!/ 2!×(9-2)! = 36

P(Two Red and Two Blue) = 10×36/1001

= 0.035964

= 0.0360

Hence, the probability that two of the balls are red and two are blue is 0.0360

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