Question

A pair of dice is rolled together till a sum of either 5 or 7 is obtained. Then the probability that 5 comes before 7 is

• A. $\frac{1}{5}$
• B. $\frac{2}{5}$
• C. $\frac{3}{5}$
• D. $\frac{4}{5}$

Answer 1

Answer: (B)

$\frac{2}{5}$

For sum of five we get $(1,4),(2,3),(3,2),(4,1)$ and for sum of seven $(1,6),(2,5),(3,4),(4,3),(5,2),(6,1)$
total number to get sum of either $5$ or $7=$ $10$
The probability that $5$ comes before $7=$ $4/10=2/5$