Mr. Jackson is rolling a number cube. Predict how many times he should roll a 5 if he rolls the die 80 times. About how many times should he roll a 2 or 5?

Question

I had this as a math problem for 7th grade. It is Compound Events and I forget how to do it. Thank you for anyone who takes the time to do it.

Answer 1

Rolling a 2 or 5 are mutually exclusive events since they cannot occur at the same time.

 

When two events, A and B, are mutually exclusive, the probability that A or B will occur is the sum of the probability of each event.

 

P(A or B) = P(A) + P(B)

 

Probability of rolling a 2 on a 6 sided dice:

P(2) = 1/6

 

Probability of rolling a 5 on a 6 sided dice:
P(5) = 1/6

 

Probability of rolling a 2 or a 5 on a 6 sided dice:

P(2 or 5) = P(2) + P(5)

P(2 or 5) = 1/6 + 1/6

P(2 or 5) = 1/3

 

Now multiply the probability by the number of rolls to predict the results.

 

Number of times he should roll a 5:

(1/6)*80 times = ~13 times

 

Number of times he should roll a 2 or 5:

(1/3)*80 times = ~ 27 times