Download Using the TI-83 to find confidence intervals

Using the TI-83 to find confidence intervals for the population mean
To find the confidence interval when
 is known or population is normal
A sample of 256 residents of a city indicated a monthly mean electric bill of $90
with a standard deviation of $24. Construct a 95% confidence interval for the
mean monthly electric bill of all residents.
Stat…Tests…#7 for Z interval…enter
For inpt: choose Stats and fill in the rest of the screen with the inputed stats. You
should find the interval is $87.06 - $92.94
To find the confidence interval for other samples
The survival times in weeks are given for 20 male rats which were exposed to a
high level of radiation.
152 152 115 109 137 88
94
77
160 165
20
128 123 136 101 62
152 83
69
125
Determine the 95% confidence interval on the mean survival time for rats.
Place your data in L1. Then go to Stat… Tests…#8 for T interval and for Inpt,
choose Data and tell the TI that the data is in L1. Fill in the rest and hit enter for
the interval of 94.57 weeks to 130.23 weeks.
To find the confidence interval for the difference of two population means
In the morning class, the mean on the first exam was 78 with a standard
deviation of 2.3 for the 57 students in the class. In the afternoon class, the mean
was 81 with a standard deviation of 5.7 for the 37 students in the class.
Determine the 90% confidence interval for the difference in the means of the two
groups.
Stat... Tests.. #0 for 2-Samp T Int... enter
For Inpt choose Stats unless you have placed the data in L1 and L2.
X bar 1 is 78 and sx1 is 2.3 with n1 as 57
Xbar2 is 81 and sx2 is 5.7 with n2 as 37
C-level is .9
Never pool
Calculate to get an interval from -4.656 to -1.344 indicating that there is a
significant difference between the two means.
To find the confidence interval using paired data
Place the before figures in L1 and the after figures in L2. Go to the very top of L3
and punch in L1 – L2 then enter. Their differences between the entries in L1 and
the entries in L2 should show up in L3. Then do a Tint using the data in L3.