(i.) Additions and subtractions are performed from left to right.
Hence we can separate the numbers from the common unit, and replace 3 lb - I - 5 lb - 7 lb +2 lb by (3+5-7+2) lb, the additions and subtractions being then performed by means of an addition-table.
(vii.) The only exception that may be made to the above rule is that an expression involving multiplication-dots only, or a simple fraction written with the solidus, may have the brackets omitted for additions or subtractions, provided the figures are so spaced as to prevent misunderstanding.
(i.) The logical result of the commutative law, applied to a succession of additions and subtractions, is to produce a negative quantity-3s.
(vi) Distributive Law, that multiplications and divisions may be distributed over additions and subtractions, e.g.