Thank you! I am glad you liked it.

That is a great question. While stating the null hypothesis if we say that there is no difference in the average recovery time, then we will write H₀: μ = 0 where μ is the difference in the average recovery time between drug A and drug B. So, the correct mathematical notation should be H₀: μ = 0 and not H₀: μ ≠ 2.67.

However, if we will say that the difference in recovery time between drug A and drug B is not 2.67 then it can be anything (> 2.67 or < 2.67) and in such case it would be better to write it as H₀: μ ≠ 2.67. as we are not sure about any of the possibility.

Thank you, I will update that in the article too. :)