Answer: 2.120
This value is approximate.
A more accurate value is 2.119905285
Round however your teacher instructs.
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Step-by-step explanation:
A 95% confidence interval means 0.95 is the area of the main central body, while the remaining 0.05 is the area of both tails combined.
The left tail has area 0.05/2 = 0.025
On your TI84 calculator, press the button labeled "2ND". Then press the "VARS" key.
Scroll down to "invT" which is the 4th option.
Then you'll type in the following
invT(0.025, 16)
The 0.025 is the area in the left tail mentioned at the top, while 16 is the degrees of freedom (because n-1 = 17-1 = 16)
The result of that calculation is approximately -2.119905285
Unfortunately, your teacher did not provide rounding instructions. But I'll round to three decimal places to get -2.120
Remove the negative sign to get the final answer 2.120
Extra info:
P(-2.120 < t < 2.120) = 0.95 approximately when the degrees of freedom is 16.