BIDMAS [ sometimes called BODMAS or even BEDMAS] is a Mnemonic to remind people of the order in which calculations with mixed operations should be worked out http://www.bbc.co.uk/bitesize/ks3/maths/number/order_operation/revision/2/ so even without brackets - there is an order in which to carry out the numerical calculations Multiplications are...
By my estimation this question has been asked at least 4x4+4x4+4-4x4 (that is, 20) times and every time the same discussion ensues. Brackets are always implicit since there is a well defined order of operations in arithmetic.
It's BOdMAS, called BIDMAS now and defines the order in which operations have to be done, especially if no brackets are shown - Brackets, indices, division, multiplication, addition and finally subtraction.