For example, let's say I'm using a one-tailed t-test to see if a box of Lucky Charms cereal has more than 100 marshmallows. I know the consequences of using a one-tailed t-test and how it wouldn't be appropriate here. However, if my t-value is -2 and there are way less marshmallows than my hypothesis, when doing the one-tailed test and I use a t-value calculator like this, it doesn't even ask which tail I want to use. So if I put in -2 and maybe a df of 9, the P-value is 0.038, which is significant. So when Wikipedia says "values in the other direction are considered not significant", what does this mean exactly? How do I correct my 0.038 to make it representative of a one-tailed t-test on the other tail - I was thinking would you say 100-0.038 to get a P-value of 99.962? Thanks so much.

For example, let's say I'm using a one-tailed t-test to see if a box of Lucky Charms cereal has more than 100 marshmallows. I know the consequences of using a one-tailed t-test and how it wouldn't be appropriate here. However, if my t-value is -2 and there are way less marshmallows than my hypothesis, when doing the one-tailed test and I use a t-value calculator like this, it doesn't even ask which tail I want to use. So if I put in -2 and maybe a df of 9, the P-value is 0.038, which is significant. So when Wikipedia says "values in the other direction are considered not significant", what does this mean exactly? How do I correct my 0.038 to make it representative of a one-tailed t-test on the other tail - I was thinking would you say 1-0.038 to get a P-value of .962? Thanks so much.