Multiple choice

An urn contains 9 red balls and p green balls. If the probability of picking a red ball is thrice that of picking a green ball, then p is equal to

  1. 6

  2. 7

  3. 2

  4. 3
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The probability of picking a red ball is 9 / (9 + p) and a green ball is p / (9 + p). Given 9 / (9 + p) = 3 * (p / (9 + p)), we get 9 = 3p, so p = 3.

AI explanation

The probability of picking a red ball is 9 divided by the total number of balls (9 + p), and the probability of picking a green ball is p divided by (9 + p). According to the problem, 9 / (9 + p) = 3 * (p / (9 + p)). Solving this equation, we cancel the denominators and divide by 3 to get p = 3.

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