Probability - Problem 5- Question

  • A bag contains 5 red balls and 3 green balls.
  • Two balls are drawn from the bag without replacement.
  • What is the probability that both balls are green?

Probability - Problem 5- Solution

  • Step 1: Determine the total number of balls in the bag: 8 (5 red + 3 green)
  • Step 2: Determine the number of ways to choose 2 green balls from 3:
    • Combination formula: nCr = n! / [(n - r)! * r!]
    • n = 3 (number of green balls), r = 2 (number of balls drawn)
    • nCr = 3! / [(3 - 2)! * 2!] = 3
  • Step 3: Determine the number of ways to choose any 2 balls from 8:
    • Combination formula: nCr = n! / [(n - r)! * r!]
    • n = 8 (total number of balls), r = 2 (number of balls drawn)
    • nCr = 8! / [(8 - 2)! * 2!] = 28
  • Step 4: Calculate the probability: P(2 green balls) = (number of ways to choose 2 green balls) / (number of ways to choose any 2 balls)
    • P(2 green balls) = 3 / 28 = 0.107

Probability - Problem 6- Question

  • A fair die is rolled 3 times.
  • What is the probability that the sum of the numbers obtained is 15?

Probability - Problem 6- Solution

  • Step 1: Determine the total number of outcomes when a die is rolled 3 times: 6^3 = 216
  • Step 2: Find the number of favorable outcomes where the sum of the numbers is 15:
    • Possible combinations: (4,5,6), (5,4,6), (5,5,5), (5,6,4), (6,4,5), (6,5,4), (6,6,3)
    • Total number of favorable outcomes: 7
  • Step 3: Calculate the probability: P(sum of numbers = 15) = (number of favorable outcomes) / (total number of outcomes)
    • P(sum of numbers = 15) = 7 / 216 ≈ 0.0324

Probability - Problem 7- Question

  • A bag contains 5 red balls, 3 green balls, and 2 blue balls.
  • Three balls are drawn from the bag without replacement.
  • What is the probability that exactly 2 balls are red?

Probability - Problem 7- Solution

  • Step 1: Determine the total number of balls in the bag: 10 (5 red + 3 green + 2 blue)
  • Step 2: Determine the number of ways to choose exactly 2 red balls:
    • Combination formula: nCr = n! / [(n - r)! * r!]
    • n = 5 (number of red balls), r = 2 (number of red balls drawn)
    • nCr = 5! / [(5 - 2)! * 2!] = 10
  • Step 3: Determine the number of ways to choose any 3 balls from 10:
    • Combination formula: nCr = n! / [(n - r)! * r!]
    • n = 10 (total number of balls), r = 3 (number of balls drawn)
    • nCr = 10! / [(10 - 3)! * 3!] = 120
  • Step 4: Calculate the probability: P(2 red balls) = (number of ways to choose 2 red balls) / (number of ways to choose any 3 balls)
    • P(2 red balls) = 10 / 120 = 0.0833

Probability - Problem 8- Question

  • In a box, there are 5 red balls, 3 green balls, and 2 blue balls.
  • Two balls are chosen at random from the box with replacement.
  • What is the probability that both balls are red?

Probability - Problem 8- Solution

  • Step 1: Determine the total number of balls in the box: 10 (5 red + 3 green + 2 blue)
  • Step 2: Calculate the probability of drawing a red ball: P(red ball) = (number of red balls) / (total number of balls)
    • P(red ball) = 5 / 10 = 0.5
  • Step 3: Calculate the probability of drawing two red balls with replacement = P(red ball) * P(red ball)
    • P(both balls are red) = 0.5 * 0.5 = 0.25