Please Help Me With These Two Way Tables For Math!!!

Question

The two way table below shows the amount of time students spent studying for their Chemistry test and the grade they earned on the test.

	0 - 50	51 - 70	71 - 90	91 - 100	Totals
0 - 1 Hour	7	12	0	1	20
1 - 2 Hours	4	5	12	8	29
2 - 3 Hours	1	4	18	22	45
More Than 3 Hours	0	3	18	15	36
Totals	12	24	48	46	130

What is the probability that a randomly selected student will study for one to two hours?

 What is the probability that a randomly selected student will study more than three hours and earn a 71 to 90?

 What is the probability that a randomly selected student will earn a 91 - 100 given they study for two to three hours?

Answer 1

In looking at the 2nd row, we ca see that the total number of people who studied 1 - 2 hours was 29. The total number of students was 130. So the probability that a randomly selected student will study for one to two hours is 29/130.

The total number of students who studied more than 3 hours AND earn 71 - 90 is found looking at the 4th row and the third column. The intersection of those is the number 18. That means 18 people studied more than 3 hours and got a 71 - 90 score. Since the total number of students is 130, the probability that a randomly selected student fits in that category is 18/130 = 9/65.

The last problem specifies that you are ONLY considering students who studied 2 - 3 hours. That means you will ONLY consider the data in the 3rd row. The number in that row who scored 91 - 100 was 15. There were a total of 36 students in that row, so the probability was 15/36 = 5/12