Question

An urn contains $7$ red and $3$ black balls. Two balls are drawn without replacement. What is the probability that the second ball is red if it is known that the first ball drawn is red.

Answer 1

Probability$=\frac{C_1^7\times C_1^6}{C_2^{10}}=\frac{7\times 6}{5\times 9}=\frac{14}{15}$