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# In a shop there are 20 customers 18 of whom will make a purchase If three customers are selected one at a time at random what is the probability that all will make a purchase?

###### Wiki User

###### September 29, 2009 9:10AM

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

## Related Questions

###### Asked in Probability

### Alternate Wordings for 'In a shop there are 20 customers 18 of whom will make a purchase. If three customers are selected one at a time at random what is the probability that all will make a purchase?

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

###### Asked in Probability

### What distinguishes a probability sample from a non probability sample?

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.

###### Asked in Statistics, Probability

### What is the difference between simple random sampling and systematic random sampling?

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.)
• Simple random sample requires that each individual is
separately selected but systematic random sample does not selected
separately.
• 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.