Question

$20$ cards numbered $1,2,3,...,20$ are put in a box and mixed thoroughly. Shashi draws a card from the box. Find the probability that the number on the card is divisible by $3$

Answer 1

Finding the probability that the number on the card is divisible by $3$.

Let $\text{P}\left(\text{E}\right)$ be the probability that the number on the card is divisible by $3$.

Total number of cards$=20$

$\therefore$Number of possible outcomes$=20$

Outcomes with numbers divisible by $3$.$=3,6,9,12,15$ and $18$

$\therefore$Number of favourable outcomes$=6$

We know that $\text{P}\left(\text{E}\right)\text{=}\frac{\text{Number of favourable outcomes}}{\text{Number of possible outcomes}}$

So, $\text{P}\left(\text{E}\right)$$=\frac{6}{20}$

$=\frac{3}{10}$

Hence, probability that the number on the card is odd$=\frac{\mathbf{3}}{\mathbf{10}}$