# One-tailed vs. two-tailed t-test and P level

In a two-tailed t-test for a P of 0.1 and a one-tailed test for a P of 0.05, is the t value to show significance the same? I understand that the two-tailed test is looking for significance at either end on the curve and the one-tailed is looking for significance in only one direction, in fact, that is why I ask the question.

In two-tailed situation where the type I error rate, $\alpha$, is set at 10%, the 10% is evenly placed at the two ends, cutting at the first 5% and the last 5% of the t-distribution.
In one-tailed with $\alpha$ is set at 5%, this 5% will just be placed at one end.
• I don't know if this is the place to ask (I didn't want to create redundant questions) but I wonder if a maximum P-value for one-sided is half of the P-value two-sided t-test? To clarify, I am doing a fitting with lsfit function in R but I only want the t-statistic of positive side – Fred Apr 21 '15 at 22:49