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18/20 x 17/19 x 16/18 = 4896/6840, or around 71.6%.

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Here is another way to phrase the question: If 18 out of 20 customers make a purchase in a shop, and three customers are selected at random, what is the probablity that all will make a purchase? Each random customer has a 18/20 chance of being one that purchased, so the probability that all three make a purchase is 18/20*18/20*18/20=.729

The probability that a year selected at random will be a leap year is 0.25.

The probability is 10 percent.

It depends on what the random variable is, what its domain is, what its probability distribution function is. The probability that a randomly selected random variable has a value between 40 and 60 is probably quite close to zero.

1/365 = 0.00274

7/2

probability = 2/7 to be exact, 28/97 (about 28.87%)

.4032

random sample

When each member of the population has the same probability of being selected as a member of the sample.

The probability is approx 0.81

6 out of 30 ie 20% or 0.2

There is only one girl out of 12 students so the probability that the girl is selected is 1/12.

This is called a random sample.

Approx 0.0287

Simple random sampling.

It is a simple random sample.

exactly 28/97, or approximately 28.87%

1/7 or approximately .142 There are 7 continents and you are choosing only 1.

Every member in the population has the same probability of being in the sample.Or, equivalently, every set of the given sample size has the same probability of being selected.

The probability of selecting 1 female at random is 4/8 There are now 7 students, 3 of which are female so the probability of selecting another female is 3/7 The probability two randomly selected students are female is (4/8)x(3/7)= 3/14

I believe you meant to ask: What distinguishes a random sample from a non random sample? A random sample means the selection or sampling from the population is by chance. Looking at the data, one might not be able to tell if the sample is random or selective. Consider a marketing survey which is included everytime you buy an item online. Random or non-random? It is a survey of recent customers, and probably a pretty good one. But it is not a random selection of all customers who have made purchases with clients.

That is known as a simple random sample, or SRS.

simple random sample is to select the sample in random method but systematic random sample is to select the sample in particular sequence (ie 1st 11th 21st 31st etc.)â€¢ Simple random sample requires that each individual is separately selected but systematic random sample does not selected separately.â€¢ In simple random sampling, for each k, each sample of size k has equal probability of being selected as a sample but it is not so in systematic random sampling.

If the balls are selected at random, then the probability is 12/95.