Question

Two distinct number cubes, one red and one blue, are rolled together. Each number cube has sides numbered 1 through 6.

Answer 1

Answer:

$P(E_1 or E_2) = \frac{7}{12}$

Step-by-step explanation:

Given

Two cubes of side 1 - 6

Required

Probability that the outcome of the roll is an odd sum or a sum that is a multiple of 5

First, the sample space needs to be listed;

Let $C_r$ represent the Red cube

$C_b$ represent the Blue cube

S represent the sample space

$C_r = (1,2,3,4,5,6)\\C_b = (1,2,3,4,5,6)\\S = (2,3,4,5,6,7,3,4,5,6,7,8,4,5,6,7,8,9,5,6,7,8,9,10,6,7,8,9,10,11,7,8,9,10,11,12)$S is gotten by getting the sum of $C_r$ and $C_b$

$n(S) = 36$

Calculating the Probability

Let $E_1$ represent the event that an outcome is an odd sum

$E_1 = (3,5,7,3,5,7,5,7,9,5,7,9,7,9,11,7,9,11)$

$n(E_1) = 18$

$P(E_1) = \frac{n(E_1)}{n(S)}$

$P(E_1) = \frac{18}{36}$

Let $E_2$ represent the event that an outcome is a multiple of 5

$E_2 = (5,5,5,5,10,10,10)$

$n(E_2) = 7$

$P(E_2) = \frac{n(E_2)}{n(S)}$

$P(E_2) = \frac{7}{36}$

Let $E_3$ represent the event that an outcome is an odd sum and a multiple of 5

$E_3 = E_1 and E_2$

$E_3 = (5,5,5,5)$

$n(E_3) = 4$

$P(E_3) = \frac{n(E_3)}{n(S)}$

$P(E_3) = \frac{4}{36}$

Calculating $P(E_1 or E_2)$

$P(E_1 or E_2) = P(E_1) + P(E_2) - P(E_1 and E_2)$

$P(E_1 or E_2) = P(E_1) + P(E_2) - P(E_3)$

$P(E_1 or E_2) = \frac{18}{36} + \frac{7}{36} - \frac{4}{36}$

$P(E_1 or E_2) = \frac{18 + 7 - 4}{36}$

$P(E_1 or E_2) = \frac{21}{36}$

$P(E_1 or E_2) = \frac{7}{12}$

Hence, the probability that the outcome of the roll is an odd sum or a sum that is a multiple of 5 is $\frac{7}{12}$