Question

Question 1

If we toss 3 coins, what is the probability that no tails will appear?
Answer

7/8

3/4

1/8

1/2

Question 2

If we toss 3 coins, what is the probability that exactly 1 tail will appear?
Answer

3/8

1/2

3/4

1/8

Question 3

If we toss a pair of dice, what is the probability that a sum of 7 will appear?
Answer

1/36

7/36

1/2

1/6

Answer 1

@ganeshie8

Answer 2

Q1 1-(0.5)^3 = 7/8
Q2 I'm not sure but I'm pretty certain that it's 1/8
Q3 6/36 = 1/6

Answer 3

are you sure the other answers are correct?

Answer 4

I am fairly certain but it's always good to make sure with others

Answer 5

Concentrationalizing are you going to reply to my question please do :]

Answer 6

When we have only a few amount of outcomes, we can count them out pretty easily. Let's look at all of the possibilities that arise from flipping 3 coins. H = heads, T = tails:

HHH TTT
HHT TTH
HTH THT
THH HTT

So we have 8 possibilities, so all of our probabilities are out of 8. We see that 7 of those 8 have at least 1 tails, so the probability of NO tails is 7/8

If we now look at, out of those 3 options, how many times a tails appears once, we can count and see it occurs 3 times, so we have 3/8 for question 2.

As for the dice roll, we can look at this drawing:



Okay, quite a bit going on, but I have every possibility, all 36, for a roll of two die. On the top running right and down are the sums of dice rolls on the diagonals I circled and on the left going down I have the probabilities of the dice rolls on the circled diagonals.
As you can see, I have a diagonal circled that has a number 7 next to it. If you follow that same diagonal down, you can see that the diagonal has the probability of 6/36 = 1/6