Section 244(1A)refund as a result of order ftom CIT(A)

shiza khan (20 Points)

06 July 2020  
If refund is not granted by AO within 3 mon from end of the mon in which order was recd by CIT then additional interest of 3% pa to be given on such refund..
My query is if the period consist of mon and part thereof then part thereof will be ignored
eg-if time period is 1month and 10days so since its pa toh we will take 1/12 or 40days/366..
A teacher in his book said ignore mon part thereof and take 1/12.
Is he right??
Any case law or clarification on my above query?
please tell me the correct ans with reason