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Mathematics

A die has 6 faces marked by the given numbers as shown below :

111 121 131 1 2 3\boxed{\phantom{1}1\phantom{1}}\space\boxed{\phantom{1}2\phantom{1}}\space\boxed{\phantom{1}3\phantom{1}}\space\boxed{-1}\space\boxed{-2}\space\boxed{-3}

The die is thrown once. What is the probability of getting

(i) a positive integer

(ii) an integer greater than -3

(iii) the smallest integer ?

Probability

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Answer

On a single throw of die,

Sample space = {1, 2, 3, -1, -2, -3}.

(i) Let E1 be the event of getting a positive integer, then

E1 = {1, 2, 3}.

∴ The number of favourable outcomes to the event E1 = 3.

P(E1)=No. of favourable outcomes to E1Total no. of possible outcomes=36=12.\therefore P(E1) = \dfrac{\text{No. of favourable outcomes to } E1}{\text{Total no. of possible outcomes}} = \dfrac{3}{6} = \dfrac{1}{2}.

Hence, the probability of getting a positive integer is 12\dfrac{1}{2}.

(ii) Let E2 be the event of getting a integer greater than -3, then

E2 = {-2, -1, 1, 2, 3}.

∴ The number of favourable outcomes to the event E2 = 5.

P(E2)=No. of favourable outcomes to E2Total no. of possible outcomes=56.\therefore P(E2) = \dfrac{\text{No. of favourable outcomes to } E2}{\text{Total no. of possible outcomes}} = \dfrac{5}{6}.

Hence, the probability of getting a integer greater than -3 is 56\dfrac{5}{6}.

(iii) Let E3 be the event of getting smallest integer, then

E3 = {-3}.

∴ The number of favourable outcomes to the event E3 = 1.

P(E3)=No. of favourable outcomes to E3Total no. of possible outcomes=16.\therefore P(E3) = \dfrac{\text{No. of favourable outcomes to } E3}{\text{Total no. of possible outcomes}} = \dfrac{1}{6}.

Hence, the probability of getting smallest integer is 16\dfrac{1}{6}.

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