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Cambridge IGCSE Mathematics — 0580 Extended

Topic 1.13: Number — Time, Money & Calculator

Calculator efficiency

Paper 2 is non-calculator, so E1.14 applies mainly to Papers 4 and 6. The key rule: do not round intermediate steps.

Method

  1. Enter the full calculation in one sequence where possible (use brackets).
  2. Keep the full display value for the next step — use Ans or store in memory.
  3. Round only the final answer to the required accuracy.

Interpreting the display:

  • Money: 4.8 on a money calculation usually means £4.80 — write two decimal places.
  • Time as decimal hours: 2.5 means 2 h 30 min; 3.25 means 3 h 15 min.
  • Fraction of an hour → minutes: multiply the decimal part by 60. E.g. 1.75 h = 1 h + 0.75 × 60 min = 1 h 45 min.

Calculate \(\dfrac{3.6 \times 12.5}{7.2}\) giving the answer correct to 2 decimal places.

Worked solution: 3.6 times 12.5 divided by 7.2 equals 6.25
Enter as one sequence: \(3.6 \times 12.5 \div 7.2 = 6.25\)

Time units and clocks

Conversions:

\[1\text{ hour} = 60\text{ minutes} = 3600\text{ seconds}\]

Which method?

Add/subtract times crossing the hour

Convert to minutes (or seconds), calculate, convert back.

Convert 24-hour to 12-hour

14:35 → 2:35 pm; 00:15 → 12:15 am; 12:00 → 12 noon.

A film starts at 19:45 and lasts 2 h 35 min. When does it finish?

Worked solution: 19:45 plus 2 hours 35 minutes is 22:20
Add hours, then minutes: 19:45 + 2 h 35 min = 22:20

London is 3 hours behind Dubai. When it is 14:30 in Dubai, what is the time in London?

Worked solution: 14:30 in Dubai minus 3 hours is 11:30 in London
Behind means subtract: 14:30 − 3 h = 11:30

Paper 2 (non-calculator)

Calculator skills are not tested on Paper 2, but time and money still appear. Practise mental time: 3 h 20 min = 200 min; difference from 08:50 to 11:35 = 2 h 45 min. Decimal hours: 2.25 h = 2 h 15 min.

Money and currency

Always write money to 2 decimal places unless told otherwise.

Currency conversion: use the exchange rate given in the question.

  • To convert pounds to euros when £1 = 1.18 euros: multiply by 1.18.
  • To convert euros back to pounds: divide by 1.18.

The rate is £1 = 1.18 euros. Convert £250 to euros.

Worked solution: 250 pounds times 1.18 equals 295 euros
Multiply by the rate: \(250 \times 1.18 = 295.00\) euros

Try this

A holiday costs 840 euros. The rate is £1 = 1.20 euros. Find the cost in pounds.

Show answer
Answer

  1. Euros → pounds: divide by the rate

    \[ 840 \div 1.20 \]

  2. \(1.20 \times 700 = 840\)

    \[ = 700 \]

  3. Write money to 2 d.p.

    \[ = £700.00 \]

Exam Traps

  • 2.5 hours is 2 h 30 min, not 2 h 50 min. Convert the decimal part by multiplying by 60.
  • A calculator showing 7.5 for money is £7.50, not £7.05 or £75.

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