How the placement percentage of a college / university is calculated?


My son has taken admission in B Tech in a college with good placement facilities. Please enlighten me on the calculation procedure of the percentage of successful candidates in campus recruitment.

My son has taken admission in B Tech 1st year in a deemed university. Placement rate of that university is very high. In that university if 400 student got placement out of 600 student ( example ) and management says placement rate is 94%. How management calculate the placement percentage?