2. Core Theory

This section is organised so that each idea builds directly on the one before it: we start with the three prices that define every transaction (CP, SP, MP), move to the algebraic relationship between them under a stated profit or loss, then layer on discount and successive discount, then the two classic “trick” question families (false weight, and same-SP-equal-%), then averaging across a mixed lot, the CP=100 shortcut technique, and finally the partnership link. Read the sections in order the first time through — later sections lean on the multiplying-factor habit built in Section 2.3.