How does t-statistic differ from z-score? select one:

a) the t statistic computes the standard error by dividing the standard deviation by n - 1 instead of dividing by n.
b) the t statistic uses the sample mean in place of the population mean.
c) the t statistic uses the sample variance in place of the population variance.
d) all of these are differences between t and z.

Option c

Step-by-step explanation:

In Statistics, both t and z tests are used for testing of hypothesis.

Whenever we have sample sizes >30 and when we know population std deviation sigma, we use Z test.

i.e. if sigma is known, we check whether sample size >30 then we use z test

Otherwise if population std deviation is not known, we use t test.  

Even if population std deviation is known, if n <30 we use t test. Both use the same formula for std error.

Hence the correct option is option c.

i would need to see the dot plot : )