Conditional Probability
A fair die is rolled, what is the probability that a face with "1", "2" or "3" dots is rolled given ( or knowing) that the number of dots rolled is odd?
2/3
In one trial of flipping a coin the probability of getting heads is?
1/2
A fair die is rolled one time, find the probability of getting an odd number or a number less than or equal to 3.
2/3
A coin is tossed twice. What is the probability of getting a tail in the first toss and a tail in the second toss?
1/4
We have three similar bags B1, B2 and B3 containing 4 balls each. B1 contains 2 red and 2 blue balls, B2 contains 3 red and 1 blue balls and B3 contains 1 red and 3 blue balls. One bag is selected at random and a ball is selected at random from that bag.
What is the probability that the ball is red?
1/2
A single card is drawn from a deck. A card is selected at random, find the probability of selecting a red card.
1/2
A fair coin is tossed 5 times. What is the probability that exactly 3 heads are obtained?
0.3125
A fair die is rolled one time, find the probability of getting a 1 or a 5.
1/3
A coin is tossed and a die is rolled. What is the probability of getting a head and a 4?
1/12
Students in a math class where 40% are males and 60% are females took a test. 50% of the males and 70% of the females passed the test. What percent of students passed the test?
62%
A group of 200 Students were asked whether they played football or basketball. Among the group, 120 said they played football, 50 said they played basketball and 20 said they played both football and basketball. What is the probability that a students selected at random from the group plays football given that he plays basketball?
0.1
A fair die is rolled 7 times, find the probability of getting 6 dots exactly 5 times.
0.00187
A box contains 3 red balls, 2 green balls and 5 blue balls. A ball is drawn at random from the box. Find the probability that the ball is either green or blue.
7/10
A card is drawn from a deck of 52 cards and then replaced and a second card is drawn. Find the probability of getting a 2 and then a King.
1/169
5% of a population have a flu and the remaining 95% do not have this flu. A test is used to detect the flu and this test is positive in 95% of people with a flu and is also (falsely) positive in 1% of the people with no flu.
If a person from this population is randomly selected and tested, what is the probability that the test is positive?
5.7%
A single card is drawn from a deck. A card is selected at random, find the probability of selecting a queen given that it is a heart.
1/13
A factory produces tools of which 98% are in good working order. Samples of 1000 tools are selected at random and tested. Find the standard deviation of the number of tools in good working order in these samples.
4.43
In a school of 100 students, 50 play football, 20 play basketball and 10 play both football and basketball. If a student is selected at random, what is the probability that he/she plays at least one of the two sports?
1/10
A poll found that 25% of the people in a certain country have heart problems. If three people are selected at random, find the probability that all three have heart problems.
0.0156
A die is rolled, find the probability that an even number is obtained.
1/2
A die is rolled, find the probability that an even number is obtained knowing the number is greater than 3.
2/3
Find the probability that at least 5 heads show up when a fair coin is tossed 7 times.
0.22656
A single card is drawn from a deck. Find the probability of an 8 or a heart.
7/13
A jar has 3 blue balls, 2 white balls and 5 red balls. A ball is selected at random and the color noted then replaced back inside the jar. A second ball is selected its color noted and replaced back inside the jar. A third ball is selected and its color noted. What is the probability of selecting a blue ball, then a white ball and then a blue ball.
9/5000
Which of these numbers cannot be a probability?
(-0.00001, 0.5, 1.001, 0, 1, 20%)
-0.00001 and 1.001