Chapter Revision Summary

Before moving on to the next chapter, make sure you can, without referring back to any notes, do the following five things from memory: (1) write down the SI formula and all three of its rearrangements; (2) state the half-yearly and quarterly compounding adjustment rule and apply it without hesitation; (3) reproduce the CI–SI difference formulas for both 2 years and 3 years, along with the one-line reasoning for why each formula works; (4) distinguish the SI-installment (accumulated-value) formula from the CI-installment (present-value) formula and know which one a given question is asking for; and (5) recognise population growth and depreciation as CI with a plus sign and a minus sign respectively.

If you struggled with any single one of Sets A or B above, do not simply re-read the theory — instead, re-derive the relevant formula from first principles on paper once, and then attempt three to four fresh numerical examples of your own construction (pick your own P, R, and T values and work them through by hand). This chapter rewards repetition of the underlying pattern far more than memorisation of any one worked example, precisely because the same handful of formulas gets recycled across dozens of superficially different question phrasings in the actual exam. Once Sets A and B both feel comfortable within their target time limits, you are ready to move on to compound applications of this chapter inside Data Interpretation sets, where CI and SI often appear as one sub-question among several built around the same table or graph.