India's Adani Group may be spending $3-3.5 billion to buy shares from public investors in Holcim's Indian assets Ambuja Cements and ACC. The group announced on Sunday that it was acquiring Switzerland-based Holcim’s entire stake in Ambuja Cements and ACC through an offshore special purpose vehicle.The value for the Holcim stake and open offer consideration is around $10.5 billion. This is the largest ever acquisition by Adani Group and India’s largest-ever merger and acquisition transaction in the infrastructure and materials space. Holcim, through its subsidiaries, holds 63.19 percent in Ambuja Cements and 54.53 percent in ACC.“The corresponding offer share prices of Rs 385 for Ambuja Cement and Rs 2,300 for ACC translate into cash proceeds of CHF 6.4 billion (Swiss Franc) for Holcim,” Holcim said.Ambuja Cements stock closed at Rs 358.80 on Friday while ACC shares ended at Rs 2,113.70 on the BSE.An open offer is an offer made by the acquirer to the company's shareholders, inviting them to tender their shares in the company at a particular price. The primary purpose of an open offer is to provide an exit option to the company's shareholders owing to a change in control or substantial acquisition of shares occurring in the company.Also Read | LIC shares trade at discount in grey market ahead of May 17 listingAn open offer is triggered when an acquirer, who holds less than 25 percent shares or voting rights in a company, agrees to acquire shares or acquires shares wherein the existing shareholding would entitle him to exercise 25 percent or more shares or voting rights in the company. The acquirer will need to make an open offer before acquiring such additional shares.Some market participants believe that even as the open offer is made, how much of it would be accepted by the shareholders is a key monitorable.“Going by the latest reported shareholdings, the minimum acceptance ratio for ACEM (Ambuja Cements) is 71 percent and ACC is 57 percent, considering a minimum offer size of 26 percent in each company,” said Abhilash Pagaria, Head - Alternative & Quantitative Research, Edelweiss Securities. It is quite early to calculate the likely final acceptance. However, very preliminary analysis shows approximately 85 percent acceptance in Ambuja Cements and over 75 percent acceptance in ACC, he said.However, if the market prices for respective companies remain higher as compared to the open offer price, then the acceptance would be 100 percent, he pointed out.About 35.46 lakh shares or 0.18 percent equity of Ambuja Cements, worth Rs 130.4 crore, have already changed hands on the exchanges on Monday.After the deal, PhillipCapital upgraded its rating on shares of Ambuja Cements to ‘buy’ and also raised its target price on the stock to Rs 440. For ACC, the brokerage firm has maintained its ‘buy’ call on the stock but raised its target price to Rs 2,850 per share.Shares of Ambuja Cements were trading 4 percent higher at Rs 373.2 on BSE, while ACC stock jumped 7.6 percent at Rs 2,274.25.Catch up on all LIVE stock market updates here.