Chapter Summary

Key Facts

• A ratio compares quantities of the same kind: same unit first, then divide every part by the HCF.
• A rate compares different kinds; a unit rate makes two of them comparable.
• $D = S \times T$, and average speed is always total distance $\div$ total time.
• Simple interest $I = \dfrac{PRT}{100}$ with $T$ in years; total $A = P + I$.
• Hire purchase total $=$ deposit $+$ instalments, always above the cash price.
• Singapore GST is 9%; commission is taken off the SGD before converting.