Question
Five horses are in a race. Mr. $$A$$ selects two of the horses at random and bets on them. The probability that Mr. $$A$$ selected the winning horse is
A.
$$\frac{2}{5}$$
B.
$$\frac{4}{5}$$
C.
$$\frac{3}{5}$$
D.
$$\frac{1}{5}$$
Answer :
$$\frac{2}{5}$$
Solution :
Let 5 horses are $${H_1},$$ $${H_2},$$ $${H_3},$$ $${H_4},$$ and $${H_5}.$$ Selected pair of horses will be one of the 10 pairs $$\left( {{\text{i}}{\text{.e}}{\text{.;}}{{\text{ }}^5}{C_2}} \right):{H_1}{H_2},$$ $${H_1}{H_3},$$ $${H_1}{H_4},$$ $${H_1}{H_5},$$ $${H_2}{H_3},$$ $${H_2}{H_4},$$ $${H_2}{H_5},$$ $${H_3}{H_4},$$ $${H_3}{H_5},$$ and $${H_4}{H_5}.$$
Any horse can win the race in 4 ways.
For example : Horses $${H_2}$$ win the race in 4 ways $${H_1}{H_2},$$ $${H_2}{H_3},$$ $${H_2}{H_4},$$ and $${H_2}{H_5}.$$
Hence required probability $$ = \frac{4}{{10}} = \frac{2}{5}$$