Question

The table below gives the typical number of days of rainfall in Fall and Spring in Death Valley, California.

Fall (Event F)

Spring (Event S)

Rain (Event R) 7 6
No Rain or Dry (Event D) 115 116

Given the fact that it rained one day in the Fall or the Spring, how much more likely is it that the day it rained was in the Fall?

1/122
1/365
1/13
1/244

Answer 1

1/13

Explanation:

P(Fall/Rained) = 7/(7+6) = 7/13

P(Spring/Rained) = 6/(7+6) = 6/13

More likely by a probability of:

7/13 - 6/13 = 1/13

Answer 2

Explanation:

Step 1: Find the probability of it raining in both of the months

Fall →
`(7)/(7+6)` →
`(7)/(13)`

Spring →
`(6)/(7+6)` →
`(6)/(13)`

Step 2: Find how much more likely it rained in Fall

`(7)/(13) - (6)/(13)`

`(1)/(13)`

Answer: Option C,
`(1)/(13)`