My chemistry teacher told me that the formulas for each group were as follows

Alkane - CnH2n+2

Alkene - CnH2n

Alkyne - CnH2n-2

Online and in my textbook however, it says that alkynes have only one less hydrogen than alkanes which would make the formula CnH2n+1. (They mentioned something about the double bonds effecting the number of hydrogens but I'm not sure how many would have to be reduced in order for it to work. *I do understand that the alkanes have 1 single C-C bond; Alkenes have 1 double C=C bond; and that alkynes have 1 C---C triple bond.)

I have a test on this and do not know which one to trust, my teacher, or the textbook.

If anyone could give me a straightforward definition/formula and a simple example it would be greatly appreciated! :) thank you!