Statistics i need help

Question

Driver Intoxicated	Pedestrian Intoxicated
Yes	yes
no	41	80
	275	589

above the 80 No is in that box. 

If two different pedestrian deaths are randomly selected, find the probability that they both involved pedestrians that were not intoxicated.

Report the answer rounded to four decimal place accuracy.

Answer 1

Hi Marisol,

To compute this probability, you first need the total number of non-intoxicated pedestrians. Then, you need the total number of deaths. So, add up the "no" column:

No: (80 + 589) = 669

Then, add up the total of all cells:

TOTAL: (41 + 275 +80 +589) = 985

Once you have those two values, you can compute the initial probability that one randomly selected death involved a non-intoxicated pedestrian by dividing:

P1 = 669/985 = 0.6792

Now, the question asked you about probability of two different deaths. That means we are randomly drawing a death again. Now, since we assume the first death involved a sober pedestrian, we have to subtract one from both the number of sober pedestrians and one from the total, then divide the results.

Sober Pedestrians= 668

Total Deaths = 984

P2= 668/984 = 0.6789

Now, we can use the Multiplication Rule. (I'll call the final probability PF)

PF= P1 * P2

PF= (0.6792*0.6789)

PF= 0.4611

I hope this helps.