Confused on One tail and Two Tail T Table

So on this problem question:

For a sample size of 17, with a mean of 116.23 and a variance of 245.55, the width of a 90% confidence interval using the appropriate t-distribution is closest to:

So we simply know the DF is 16

What confuses me is:

  1. If it isn’t specified as one tail or two tail, does the default is two tail?

  2. If it’s two tail, do we check the " Level of significance for two tail table" at

a. check the value at 10% / 2 = 5% = 0.05 significance = 2.120


b. check the value at 10% = 0.1 significance = 1.746

  1. If it’s one tail, do we simply check the 10% value at one tail table?

yes me too how do we know its two tailed? in this chapter it has been a constant when we are presented with some tables of 1 tailed significance and then the problem is two tailed, and things like that.

If you are asked to calculate a Confidence Interval, you can bet your life you must use a two-tailed test.

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