(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.

Additions and **subtractions** are simple.

8d., on the grouping system, we split up each quantity into its denominations, perform the **subtractions** independently, and then regroup the results as the " remainder " £6, 2s.

Starting from the dividend, we in theory keep on subtracting the unit, and count the number of **subtractions** that have to be performed until nothing is left.