Half, A half
Incorrect : He came here at seven and a half.
Correct . He came here at half past Seven.
Incorrect : I took half past two hours to do the work.
Correct : I took two hours and a half to do the Work.
Note: In telling time, we use the expressions “half past one', 'half past two’ etc. to mean 1.30, 2.30 etc. But when we refer to a duration or length of time, we use ‘one and a half hours' to mean 'one hour and thirty minutes."