Yes. Section 203 of the MBTA provides in part that:
The modified gross receipts of a unitary business group is the sum of modified gross receipts of each person, other than a foreign operating entity or [an insurance company or financial institution], included in the unitary business group less any modified gross receipts arising from transactions between persons included in the unitary business group.
MCL 208.1203(3). A taxpayer calculates its modified gross receipts tax base by determining its gross receipts and then subtracting "purchases from other firms," a term that is defined at MCL 208.1113(6). Therefore, each member of a unitary business group must subtract any "purchases from other firms" in order to arrive at its individual modified gross receipts, whether those qualifying purchases were made from fellow group members or from outside companies. In addition, section 511 of the MBTA specifically provides that, in filing the required combined return, all transactions between members of a unitary business group are to be eliminated from the business income tax base, the modified gross receipts tax base, and the apportionment formula. MCL 208.1511. "All transactions" includes those transactions meeting the definition of "purchases from other firms," as well as other kinds of transactions between group members.