Q. Two dice are rolled one after the other. The probability that the number on the first is smaller than the number on the second is

A) $\frac{1}{2}$
B) $\frac{3}{4}$
C) $\frac{7}{18}$
D) $\frac{5}{12}$
Explanation

(d)
Let $A =$Event of getting $i$ on first dice
and $B =$Event of getting more than $i$ on second dice
$\therefore$ Required probability $= \sum_{i = 1}^{5}{P(A_{i}} \cap B_{1})$
$= \frac{1}{6}\lbrack P\left( B_{1} \right) + P\left( B_{2} \right) + P\left( B_{3} \right) + P\left( B_{4} \right) + P\left( B_{5} \right)\rbrack$
$= \frac{1}{6}\left\lbrack \frac{5}{6} + \frac{4}{6} + \frac{3}{6} + \frac{2}{6} + \frac{1}{6} \right\rbrack$
$= \frac{15}{36} = \frac{5}{12}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.