# Probability Word Problem

• Apr 21st 2010, 06:23 PM
eri123
Probability Word Problem
I can't seem to come up with the correct answer. Any help would be appreciated. Thanks!

Problem: You ask a neighbor to water a sickly plant while you are on vacation. Without water, the plant will die with a probability of 90%. With water, it will die with a probability of 30%. You are 95% certain the neighbor will remember to water the plant. You come back from vacation and the plant is dead. What is the probability the neighbor forgot to water it?
• Apr 21st 2010, 08:10 PM
mr fantastic
Quote:

Originally Posted by eri123
I can't seem to come up with the correct answer. Any help would be appreciated. Thanks!

Problem: You ask a neighbor to water a sickly plant while you are on vacation. Without water, the plant will die with a probability of 90%. With water, it will die with a probability of 30%. You are 95% certain the neighbor will remember to water the plant. You come back from vacation and the plant is dead. What is the probability the neighbor forgot to water it?

Draw a tree (hah! hah!) diagram and use Bayes Theorem:

$\frac{(0.05)(0.9)}{(0.05)(0.9) + (0.95)(0.3)} = ....$