Time, Money & Using a Calculator
MathematicsΒ· 1.14, 1.15, 1.16Β· 25 min read
1. Time Calculations: Clocks, Timetables & Time Zonesβ β ββββ± 8 min
12-hour vs 24-hour clock conversion
12-hour clock uses AM/PM to distinguish morning and afternoon times. 24-hour clock uses 00:00 to 23:59 with no AM/PM notation. Add 12 to 12-hour PM times (1PM to 11PM) to convert to 24-hour format.
Example:
7:30 PM = 19:30, 12:15 AM = 00:15
You will also be required to interpret timetables (e.g. bus, train schedules) and calculate time zone differences. Use 1 year = 365 days for all time-related questions unless stated otherwise.
A flight departs London at 14:45 (GMT) and arrives in Dubai, which is 4 hours ahead of GMT, after a 6 hour 30 minute flight. What is the local arrival time in Dubai in 24-hour format?
- 1
- Calculate arrival time at GMT first: 14:45 + 6 hours 30 minutes = 21:15 GMT
- 2
- Add the 4 hour time difference for Dubai: 21:15 + 4 hours = 01:15 the next day
- 3
Final answer: 01:15
Exam tip:
Always specify if your time answer falls on the next day if relevant, and double check if the question asks for 12 or 24 hour format.
2. Money Calculations & Currency Conversionβ β ββββ± 8 min
Exchange rate
The value of one currency relative to another. If 1 GBP = 1.25 USD, multiply GBP amounts by 1.25 to get USD, divide USD amounts by 1.25 to get GBP.
Example:
Β£50 = 50 * 1.25 = \$62.50
All money calculations should be given to 2 decimal places for currencies that use cents/pence, unless the question specifies otherwise.
The exchange rate is 1 EUR = 0.88 GBP. A tourist wants to convert 350 EUR to GBP. How much GBP will they receive, to the nearest penny?
- 1
- Multiply the EUR amount by the exchange rate to get GBP
- 2
- 3
- Add 2 decimal places for standard currency notation: Β£308.00
Exam tip:
Never round currency values before the final step, as this can lead to small inaccuracies that fall outside the accepted mark range.
3. Efficient & Accurate Calculator Useβ βββββ± 7 min
β Calculator OK
Calculator skills are only assessed on Core Paper 3 (calculator allowed). You should be familiar with BIDMAS order of operations to enter calculations correctly, and know how to use your calculator's fraction, decimal, and negative number functions.
Calculate the value of using a calculator, giving your answer correct to 2 decimal places.
- 1
- Enter the calculation correctly, using brackets to group the numerator and denominator to follow BIDMAS rules:
- 2
- 3
- 4
- Round to 2 decimal places: 8.85
Exam tip:
Always cross-verify your calculator answer with a rough mental estimate to catch accidental input errors, e.g. 40 divided by 5 is 8, so 8.85 is a reasonable answer for the example above.
4. Common Pitfalls
Wrong move:
Converting 12 PM to 24-hour by adding 12, resulting in 24:00 instead of 12:00
Why:
12 PM is midday, so it stays 12:00 in 24-hour format, while 12 AM is midnight (00:00)
Correct move:
Only add 12 to PM times from 1 PM to 11 PM; leave 12 PM as 12:00 and 12 AM as 00:00
Wrong move:
Rounding currency values at intermediate steps before the final answer
Why:
Early rounding accumulates small errors that can make your final answer fall outside the accepted mark range
Correct move:
Store all intermediate values in your calculator's memory, only round the final answer to 2 decimal places
Wrong move:
Subtracting time zone differences instead of adding them (or vice versa) for arrival time calculations
Why:
Confusion about whether the destination is ahead of or behind the origin time zone
Correct move:
Add the time difference if the destination is ahead, subtract if it is behind; test with a simple example if unsure
Wrong move:
Entering calculator calculations without brackets where required, e.g. entering instead of grouping sums in brackets
Why:
Violates BIDMAS order of operations, leading to calculation of the wrong value
Correct move:
Always use brackets to group parts of the calculation that need to be performed first, as per the question's structure
Wrong move:
Giving time answers in the wrong format, e.g. 12-hour when 24-hour is requested, or omitting AM/PM for 12-hour answers
Why:
Failure to read question instructions carefully
Correct move:
Double check the question's required output format before writing your final answer
5. Quick Reference Cheatsheet
Concept | Key Rule | Example |
|---|---|---|
12 to 24-hour conversion | Add 12 to PM times (1PM-11PM); 12AM=00:00, 12PM=12:00 | 3:20PM = 15:20, 12:45AM=00:45 |
Currency conversion | Multiply to convert from base currency, divide to convert to base currency | 1GBP=1.25USD: Β£20 = \50 = Β£40 |
Calculator use | Use brackets to follow BIDMAS; keep intermediate values in memory | (12 + 8)/(5 - 1) = 5, not 12 + 8/5 - 1 = 12.6 |
Time zones | Add difference if destination is ahead, subtract if behind | GMT + 3 hours: 15:00 GMT becomes 18:00 local time |
6. Frequently Asked
Can I use a calculator for time and money questions on Paper 1?
No, Paper 1 is a non-calculator Core paper. Calculator use is only permitted for Core Paper 3 and Extended Paper 4.
How many decimal places should I use for money answers?
Unless the question explicitly states otherwise, all money answers should be rounded to 2 decimal places for currencies that use cents or pence.
What is the rule for converting PM times to 24-hour format?
Add 12 to the hour value for all PM times between 1 PM and 11 PM. 12 PM (midday) stays 12:00, and 12 AM (midnight) converts to 00:00.
Going deeper
What's Next
Now that you have mastered time, money and calculator skills, you are ready to move on to more complex number topics in the CIE IGCSE Maths 0580 Core syllabus. These foundational skills are used across many other topics including percentages, statistics, and practical problem-solving questions that appear frequently on Core Paper 3. Be sure to practice past paper questions to reinforce your accuracy, especially for currency conversion and time zone problems where small errors can lead to lost marks. You should also fully familiarize yourself with your calculator's functions ahead of the exam to avoid wasting time during the test.