### CFA Practice Question

There are 985 practice questions for this topic.

### CFA Practice Question

As part of a promotion for a new type of cracker, free trial samples are offered to shoppers in a local supermarket. The probability that a shopper will buy a packet of crackers after testing the free sample is 0.20. Different shoppers can be regarded as independent trials. Let X be the number among the next twenty shoppers who buy a packet of the crackers after tasting a free sample. The standard deviation of X is ______.

A. 4.00
B. 3.20
C. 1.79

X, the number of shoppers who buy a packet of crackers after tasting a free sample, has a binomial distribution with parameters n = 20 and p = 0.2. The standard deviation of X is [np(1-p)]1/2 = 1.79.

User Comment
cleopatraliao hv to read the question more carefully--"next twenty shoppers..."
Oregon same, i calculated the variance and stopped there
Debashree same man...i need to remeber np*(1-p) is variance and not std dev.
gyee2012 Probability Calc

Variance = p (p-1) * n
Std = Var^1/2