Question

A box contains 3 red and 4 blue marbles. Two marbles are drawn without replacement. What is the probability that the second marble is red if it is known the first marblel is red?

(a) \(\frac {3}{7}\)

(b) \(\frac {4}{7}\)

(c) \(\frac {1}{3}\)

(d) \(\frac {1}{7}\)

I got this question in a national level competition.

My doubt is from Multiplication Theorem on Probability topic in division Probability of Mathematics – Class 12

Answer 1

Correct answer is (c) \(\frac {1}{3}\)

For explanation: Total number of marbles = 7

Probability of the first marble to be red = \(\frac {3}{7}\)

Probability of the second marble to be red without replacement = \(\frac {2}{6} = \frac {1}{3}\)