The first picture is red heart (13/54) * (12/53) * (24/52).

The second picture is a square (13/54) * (13/53) * (24/52).

The third is spades (13/54) * (13/53) * (25/52).

The fourth picture is plum blossom time (13/54) * (13/53) * (25/52).

Adding up the above, the probability is 125/954=0.0084.

This may be easier to understand. In fact, this question can also be conditional on the third card, and the answer is simpler.

Question 2: It is also a conditional probability.

Whoever shoots first has a 70% chance of being hit and a 30% chance of not being hit. When he misses it, the second person will make up for it. The probability is 70%+30%×70%=94%.

It's the same with another person, 80%+20%×70%=94%.

Question 3: The probability that eight faces appear as 5 is 1/8, and two faces are 1/64. Calculate the residual probability:

The total is 18, and there are already two 5s, so the sum of the remaining two is 8.

Possible combinations are

( 1,7)

(2,6)

(3,5)

(4,4)

(7, 1)

(6,2)

(5,3)

There are seven cases in the remaining two, so the probability is 7/64, so the total probability is (1/64)*(7/64)=7/4096.

Question 4: I haven't understood the meaning of the question yet. Let me remind you that there are 12 numbers in an hour, 60 numbers in a minute and 60 numbers in a second. So if it's a displayed number problem, there is a combination of 12×60×60, which may be the denominator.

If you understand the meaning of the topic, remember to send me a Baidu message and I will answer it for you.

Supplement: You are looking at an electronic watch (not a 24-hour clock). The order is: hours: minutes: seconds. Know that you have seen at least one "5" and ask the probability that you have seen three "5".

Imagine the six numbers on the watch display as six spaces. If one is known to be 5, it cannot be displayed at the front. Only 1 and 0 can be displayed in front, and its position probability is 1/5. Therefore, there are still four positions left. The combination of two 5s is 2 of 4, and there are six situations. If you have learned the combination, you can express it as C4, 2(2 is subscript, 4 is superscript), and each shows 5. Therefore, the total probability is (1/5) * (C4, 2) * (110) * (1/).

Question 5: The answer is 1/27.

Note: the probability of extracting things before and after is irrelevant, so you can directly calculate the second time. The second time, both cards are red 7, so the probability is 2/54. If you don't understand this, you can understand it like this:

When the first card is a 7 of diamonds, the probability that the second card is a 7 of hearts: (1/54)*( 1/53).

When the first card is 7 of hearts, the probability of the second card is 7 of diamonds: (1/54) * (1/53).

When the first one is other, the probability that the second one is red is 7: (52/54)*(2/53).

This adds up to 1/27.

Question 6: In fact, the first person has a 50% chance to break the gun, while others have a 100% chance to kill the duck. These ducks must be dead, so the probability is 100%.

But I don't think the meaning of the topic is to find probability, right? For example, how many ducks can live? The probability of the number of ducks that survive.

If the first man's gun is broken and the other four are not, if he shoots at the same time, then there is a 50% chance that a duck will survive.

If the first man's gun doesn't break, then these ducks are dead. 100% inactive