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### Course: Math for fun and glory>Unit 5

Lesson 2: Random sampling warmup

# Random sampling intuition

Created by Brit Cruise.

## Want to join the conversation?

• At Sal said it could be one of those "one in a quadrillion chances that it picked white every time." There had been about 800 trial picks at that time. Is the odds of 800 white in a row really one in a quadrillion, or close to it?
• Why does a realistic result approach a theoretical result from a top? it actually takes quite some time to go under 67%. Any ideas?
• why dont you just count the marblse ?
• You won't necessarily have the opportunity to see the marbles in the bag/cup/box/etc.
If you were to change the number of black & white marbles, and then cover up the left-hand side of the screen from a friend, you could have them guess how many of each color you put in.
• What is the website for that simulation
(1 vote)
• ye sit is larger and the moon is smaller
(1 vote)
• the probability of it being a significant departure
(1 vote)
• what does intuition even mean?
(1 vote)
• According to my psychology textbook, intuition is an effortless, automatic feeling or thought.
(1 vote)
• At , Sal says that the percentage is getting pretty close to the actual ratio. At the time, it is at about 70%. Is that considered "close" to 50% in statistics? If not, why does he describe it that way?

EDIT: Just realized that 1:1 would be 50%. Would 4:2 be 66.6% or does 70% work too?
(1 vote)
• The bottom of the cup shows 66.7% that white will be picked. Still, the percentage keeps changing. I know it is random, but it should stay within 1-2% of 66.7, but sometimes it drifts to 70%. If the pattern continued, it would forever be random, but it should stay within that 66.7% range. I don't totally know why it drifts that far off the percentage average, but why should it?
(1 vote)
• It is at 70% early on. Later, though, it definitely gets closer to 67%. The fewer we have picked, the easier some unlikely string is able to increase the percentage to 70%.
(1 vote)
• This is a little off topic, but what program does he use for that?
(1 vote)

## Video transcript

Voiceover:I have a little simulation here that saves us time. It does the random picking for us. Voiceover:Mm-hmm. Voiceover:And it allows me to start with four whites and two blacks, and I'm going to have the computer do many selections for us. Voiceover:So, this is every selection the computer's doing, the equivalent of randomly picking out a marble. It's shaking it and randomly picking it, and you see that now the percentage of white, it's getting pretty close to the actual percentage, or a 4:2 ratio, I should say, of white to black. Voiceover:So, I think I believe you now, because at the beginning, I see a lot of variation- Voiceover:Right. Voiceover:On this graph over time, and now it's kind of flat-lining. Voiceover:It's definitely, it feels like it's converging to the actual proportion, and once again, there's some chance that it didn't. We could have, it could have been just one of those one in a quadrillion circumstances (laughs) where you just kept picking a white every time, but this is consistent with the intuition, as the more trials you have, it just becomes harder and harder, the probability of it being a significant departure from the actual proportion becomes lower.