To the nearest percent what is the probability that a student who failed the exam got less than 6 hours of sleep

In order to study the relationship between the amount of sleep a student gets and his or her school performance, a researcher collected data from 120 students. The two-way frequency table shows the number of students who passed and failed an exam and the number of students who got more or less than 6 hours of sleep the night before.

The probability that a student who failed the exam got less than 6 hours of sleep can be calculated as:

Let,

L be the event of getting less than 6 hours of sleep

F be the event of failing the exam.

Then,

P (L and F) = n (L∩F) : n (F)

= (10 : 18) * 100%

= 5 : 9 * 100%

= 55.55%