Please be aware that share offered in open offer don`t qualify for long term capital gains tax ( I am assuming you ware holding these shares for more than 1 year ). When you pay tax on shares sold in open offer your Rs. 40 gain will vanish.
Very true but hardly any investor understands the catch in such open offers. If shares were purchased less than a year ago and tendered in open Offer the Short Term Capital Gains will be at the rate in which the share holder`s income falls.