Cards numbered 1 to 30 are put in a bag. A card is drawn at random from the bag. Find the probability that the number on the drawn card is
(i) not divisible by 3,
(ii) a prime number greater than 7,
(iii) not a perfect square number.
Total number of outcomes = 30.
(i) Let E1 be the event of getting a number not divisible by 3.
Out of these numbers, numbers divisible by 3 are 3, 6, 9, 12, 15, 18, 21, 24, 27 and 30.
Number of favourable outcomes = 30 − 10 = 20
$\therefore \mathrm{P}($ getting a number not divisible by 3$)=\mathrm{P}\left(\mathrm{E}_{1}\right)=\frac{\text { Number of outcomes favourable to } \mathrm{E}_{1}}{\text { Number of all possible outcomes }}$
$=\frac{20}{30}=\frac{2}{3}$
Thus, the probability that the number on the card is not divisible by 3 is $\frac{2}{3}$.
(ii) Let E2 be the event of getting a prime number greater than 7.
Out of these numbers, prime numbers greater than 7 are 11, 13, 17, 19, 23 and 29.
Number of favourable outcomes = 6
$\therefore \mathrm{P}($ getting a prime number greater than 7$)=\mathrm{P}\left(\mathrm{E}_{2}\right)=\frac{\text { Number of outcomes favourable to } \mathrm{E}_{2}}{\text { Number of all possible outcomes }}$
$=\frac{6}{30}=\frac{1}{5}$
Thus, the probability that the number on the card is a prime number greater than 7 is $\frac{1}{5}$.
(iii) Let E3 be the event of getting a number which is not a perfect square number.
Out of these numbers, perfect square numbers are 1, 4, 9, 16 and 25.
Number of favourable outcomes = 30 − 5 = 25
$\therefore \mathrm{P}$ (getting non-perfect square number) $=\mathrm{P}\left(\mathrm{E}_{3}\right)=\frac{\text { Number of outcomes favourable to } \mathrm{E}_{3}}{\text { Number of all possible outcomes }}$
$=\frac{25}{30}=\frac{5}{6}$
Thus, the probability that the number on the card is not a perfect square number is $\frac{5}{6}$.