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.
(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.