Summary — What's in This Chapter

• Time: conversions (seconds → minutes → hours → days → years), reading 12-hour vs 24-hour clocks, calculating durations, timetables, and time zones.
• Money calculations: spotting keywords (total, difference, exchange), and rounding money correctly — usually to 2 decimal places.
• Exchange rates: converting between currencies by multiplying or dividing by the given rate.
• Converting units: length, mass, and volume/capacity conversions using powers of 10.
• Squared & cubic units: why you must square or cube the conversion factor for area and volume — not just multiply once.

1. Time

Why time is "annoying" compared to normal numbers

Every other measurement in maths (length, mass, money) is based on powers of 10 — that's the decimal system. Time is not decimal. It's a leftover from ancient Babylonian counting, which is why we have 60 seconds in a minute (not 100), and 24 hours in a day (not 10). This is exactly why time trips people up on calculators — more on that in the Exam Tips section.

12-hour clock vs 24-hour clock

Think of it like this: a 12-hour clock is like running around a circular track twice a day — once labelled AM (midnight to midday) and once labelled PM (midday to midnight). A 24-hour clock only runs around the track once, so it needs bigger numbers (00:00 to 23:59) instead of relabelling with AM/PM.

• 24-hour time always uses four digits, e.g. 09:05, not 9:5.
• Midnight = 00:00 (24hr) = 12:00am (12hr)
• Midday = 12:00 (24hr) = 12:00pm (12hr)
• Anything from 1pm onwards: add 12 to the hour. E.g. 5:32pm → 17:32.

Reading an analogue clock

An analogue clock always works in 12-hour time. The short hand points to the hour (each number = 1 hour). The long hand points to the minutes (each number = 5 minutes, since 12 × 5 = 60). Some clocks add small tick marks between the numbers for individual minutes.

Calculating durations — the "chunks of time" method

This is the single most useful technique in the whole time section. Don't try to subtract times directly (11:23 − 6:32 does not work like normal subtraction because of the 60-minute wraparound). Instead, break the journey into friendly chunks:

Bus and train timetables

Timetables almost always use the 24-hour clock, written as 4 digits with no colon (e.g. 0816 means 08:16). Each column represents a different bus/train. The times listed are usually departure times at each stop, except the very last stop, which shows the arrival time.

Time zones

Different places on Earth see the sun at different times, so clocks are set differently depending on longitude. If a country is "ahead," its clock shows a later time than yours right now; if it's "behind," its clock shows an earlier time. The key skill is: add the time difference to move to a location ahead of you, subtract it to move to a location behind you.

2. Money Calculations

Money questions are really just wordy versions of add/subtract/multiply/divide questions. The exam skill isn't the arithmetic — it's translating the words into the correct operation, and then rounding sensibly at the end.

Reading the keywords

Money questions are also a favourite place for examiners to sneak in other topics you've learned — percentages, fractions, simple/compound interest — dressed up as a shopping or bill scenario. Always identify which "maths skill" is really being tested underneath the money context.

Rounding rules for money

For very large amounts (like the price of a car or a house), rounding to the nearest £1, £10, or £100 might make more sense — use your judgement based on the size of the numbers in the question. Some currencies (like Japanese Yen or Indonesian Rupiah) naturally involve huge numbers, so rounding to the nearest whole unit is usually appropriate there.

3. Exchange Rates

An exchange rate tells you how much one unit of currency A is worth in currency B — it's exactly the same idea as converting cm to inches, just with money. The tricky part is always deciding whether to multiply or divide.

4. Converting Between Units

Unlike time, metric units of length, mass, and capacity do follow the decimal system — so every conversion here is just multiplying or dividing by a power of 10 (10, 100, or 1000). Your only real job is figuring out which power of 10, and whether to multiply or divide.

The "does it get bigger or smaller" trick

Length

Mass

Volume / Capacity

5. Squared & Cubic Units

This is the single biggest trap in this whole chapter — and it's worth understanding properly rather than just memorising, because half-remembered rules here cause a LOT of lost marks.

Why you can't just reuse the length conversion

Imagine a square that measures 1 m by 1 m. Its area is 1 m². Now convert each side to centimetres: 100 cm by 100 cm. What's the area now? 100 × 100 = 10,000 cm² — NOT 100 cm² as you might first guess by just copying the length conversion factor. This happens because area is two-dimensional — length gets converted twice (once for each side), so the conversion factor itself must be squared. The same logic applies to volume, but conversion happens three times (length × width × height), so the factor must be cubed.

Area conversions

Volume conversions

What to Memorise

Concepts Checklist

• I know all the standard time conversions (seconds, minutes, hours, days, weeks, years)
• I know the number of days in every month, including leap years
• I can convert confidently between 12-hour and 24-hour clock times
• I can read times off an analogue clock face
• I can find the duration between two times using the "chunks of time" method
• I can read and interpret bus/train timetables
• I can convert times between time zones, knowing when to add or subtract
• I can spot keywords in money questions (total, difference, exchange) and choose the right operation
• I round money to 2 decimal places correctly, only at the final step
• I can convert between currencies using an exchange rate, choosing multiply or divide correctly
• I can convert units of length, mass, and capacity using the correct power of 10
• I understand why area conversions require squaring the length factor
• I understand why volume conversions require cubing the length factor
• I can do multi-step conversions by going through an intermediate unit

Exam Tips & Common Mistakes