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Randomly investigate the birthdays of 100 people (including the elderly, young and middle-aged, children, etc.), and find out the probability that two of them have the same birthday (can be different years)
Suppose a is one of 100 people, the probability that a's birthday is a certain date is 1 / 365, and the probability that the other person has the same birthday with him is 1 / 365, then the probability that two people have the same birthday is 1 / 365 ^ 2. If the first two people have different birthdays, then the probability that the two people's birthdays are two certain dates is 2 / 365, and the probability that the third person's birthday is a certain date is 1 / 365, Then the probability of two of the three people having the same birthday is 1 / 365 * 2 / 365 = 2 / 365 ^ 2
And so on: the probability of the 100th person having the same birthday as any of the first 99 people is 99 / 365 ^ 2, so there is the following formula
1/365^2 + 2/365^2 + 3/365^2 + …… + 99/365^2 = （1 + 2 + 3 + …… + 99)/365^2
I didn't want to forget it, but it's not difficult. Let's just forget it
The results were 4950 / 133225
Reduced to: 198 / 5329 ≈ 3.7155%
That's all
Xiao Hong drinks a cup of milk and drinks it in four times. The first time, she drinks 16% of the milk and then fills it with water; the second time, she drinks 13% of the milk and then fills it with water; the third time, she drinks half a cup and then fills it with water; the fourth time, she drinks it all in one gulp. Does Xiao Hong drink more milk or more water? What do you think?
16 + 13 + 12 = 12 + 12 = 11 = 1 A: Xiao Hong drinks as much milk as water. I think like this: take the volume of the cup as a unit of "1". First of all, it is clear that the milk has not been added, so Xiao Hong drinks a cup of milk. The second time, she adds 16% of the volume of the cup, and the third time, she adds 16% of the volume of the cup
Junior high school engineering questions
Engineering problem application related knowledge point workload = work efficiency × work time work efficiency = workload ／ work time work time = workload ／ work efficiency sum of each workload to complete a task = total workload = 11, a manuscript, a and B work together
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