Question

A number is selected at a random from the natural number upto 30. What is the probability that is not a prime number

Answer 1

Given

Natural numbers till 30.

Prime numbers = 2, 3, 5, 7, 11, 13, 17, 19, 23, 29

There are a total of 9 prime numbers out of 30

Probability of getting a prime number =

$\dfrac{10}{30}$

Probability of not getting a prime number =

$1 - \dfrac{10}{30}$

$\dfrac{30-10}{30}$

$\boxed{\boxed{\bold{\dfrac{2}{3}}}}$

                                                 

Answer 2

Answer:

• Prime Number : Those numbers which can be divided without leaving a Remainder by itself or by 1.

⋆ Prime Numbers b/w 1 to 30 :

↠ 2, 3, 5, 7, 11, 13, 17, 19, 23, 29

(Total 10 Prime Numbers in b/w 1 to 30)

$\rule{150}{1}$

$\underline{\bigstar\:\:\textsf{Probability of Getting Prime :}}$

$:\implies\sf Probability=\frac{Number \:of\:Outcomes}{Total \:Favourable \:Outcomes}$

⠀

$:\implies\sf Probability_{(Prime)}=\dfrac{10}{30}$

⠀

$:\implies\sf Probability_{(Prime)}=\dfrac{1}{3}$

⠀

$:\implies\sf Probability_{(Prime)}=0.33$

$\rule{170}{2}$

$\underline{\bigstar\:\:\textsf{Probability of not Getting Prime :}}$

$\dashrightarrow\sf\:\: Probability_{(Not\:Prime)}=1- Probability_{(Prime)}\\\\\\\dashrightarrow\sf\:\:Probability_{(Not\:Prime)}=1-0.33\\\\\\\dashrightarrow\:\:\underline{\boxed{\sf Probability_{(Not\:Prime)}=0.67}}$

⠀

$\therefore\:\underline{\textsf{Probability of not getting prime is \textbf{0.67}}}.$