Question

When a fair dice is rolled, then the probability of getting a number less than $5$ is $\frac{a}{b}$. Find the value of $a+b$.

Note: $a$ and $b$ are co-prime.

Answer 1

When a fair dice is rolled the total number of possible outcomes is 6. Let E be the required event Then the outcomes favourable to E are 1, 2, 3 and 4 i.e. 4 favourable outcomes.
$\Rightarrow P\left(E\right)=\frac{4}{6}=\frac{2}{3}$
Hence the probability of getting a number less than 5 is 2/3.

$\frac{a}{b}=\frac{2}{3}$

$a+b=2+3=5$