O Level MathematicsC1.12 Rates (exchange rates, average speed).

🔢 Mastering Rates Made Easy!

Edudent Academy
7 Dec 25

**Rates** tell us how one quantity changes with respect to another. From swapping holiday cash to timing a 100-metre sprint, rates let us compare and predict real-life situations quickly—an essential skill for O-Level exams and beyond.

Key Ideas at a Glance

  • Average speed formula:
    extspeed=distancetime ext{speed} = \frac{\text{distance}}{\text{time}}
  • Currency conversions: **amount in new currency** =  =\;(amount in original currency) ×\times (exchange rate)

Worked Example: Currency Swap & Road Trip

Problem: Sarah converts 150 USD to Singapore dollars at a rate of 1 USD = 1.32 SGD. She then drives 198 km in 2 h 15 min. Find (a) how many SGD she receives, and (b) her average speed in km/h. Solution Steps: 1. Currency conversion:
150×1.32=198 SGD150 \times 1.32 = 198\text{ SGD}
2. Change time to hours: 2 h 15 min=2.25 h2\text{ h }15\text{ min}=2.25\text{ h} 3. Average speed:
1982.25=88 km/h\frac{198}{2.25}=88\text{ km/h}
**Answer:** (a) 198 SGD, (b) 88 km/h. Practise similar questions to build speed and confidence!