Even otherwise extremely numerate people have been well-known to litter up their hands in fear at the assumed of including together times.

A system like time, i beg your pardon is not decimal, can be counter-intuitive and requires concentration.

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However, through a little bit of application, girlfriend too deserve to learn exactly how to calculate with time, and also gain confidence in manipulating hours, minutes and seconds.

Basic devices of Time

The simple units the time, which allow you to perform calculations involving time, are:

Unit Notes
Second The second is the international System the Units (SI) measurement for time. The symbol "s" is provided to signify a second. Secs are likewise commonly abbreviated to sec.
Minute 60 Seconds A minute nearly always has sixty seconds. However, an extremely occasionally (approx. Once every 18 months) a minute can have 61 seconds. These "leap seconds" are offered to store our clocks aligned come the earth"s rotation roughly the sun.
Hour 60 Minutes It is usual to talk around "half an hour" (30 minutes) and "quarter of an hour" (15 minutes).
Day 24 hours
Week 7 days It is additionally common for world to talk about a work-related week, typically 5 days (Monday - Friday) and weekends (Saturday and also Sunday).
Month 28,29, 30 or 31 days. Different months have various numbers the days. All months have actually either 30 or 31 days other than for February. February has 28 work in a typical year and an extra day in a leap year; the 29thday the February is called the leap day.
Year 12 Months A year constantly has 12 months. A year has roughly 52 weeks. A common year has actually 365 days and a leap year (occurring mainly every 4 years) has 366 days.
Decade 10 Years
Century 100 Years
Millennium 1,000 Years

Years are commonly break-up into quarters, particularly in business and education settings, with each 4 minutes 1 being 3 months or about 90 days. Quarters in a certain business or sector may not have to be the very same as those shown below:

The variety of days in a month varies. Every months have actually the same number of days each year except because that February which has actually 28 days in a common year and also 29 in a leap year.

Quarter 1 Quarter 2 Quarter 3 Quarter 4
Month Days Month Days Month Days Month Days
January 31 April 30 July 31 October 31
February 28/29 May 31 August 31 November 30
March 31 June 30 September 30 December 31

As the number of days in a month varies, this also way that the number of weeks in a month varies too.

People regularly use approximations when calculating the variety of days in months. For example, it is usual to usage the presumption that a month contains four weeks, also though just February in a typical year in reality does so.

This makes it hard to transform from months to weeks and also vice versa, unless you know which months are being used, because there is no prompt ‘conversion factor’.

Top Tip!

If you are converting between months and also weeks, the best means to perform so is via years, due to the fact that they constantly contain 12 months (even in a leap year).

To transform months to weeks, divide by 12 and multiply through 52. To transform weeks to months, divide by 52 and multiply by 12.

The answers you acquire will be good approximations.

Writing Time

There are many different ways to create time. The easiest (digital) form is as composed hh.mm or hh:mm, for instance 10.21 or 10:21.

Hours might be either split into 24 (known together the 24-hour clock) or two lots of 12 (often referred to as the 12-hour clock).

When making use of the 24-hour clock, the 24 hour bike starts with the moment 00:00 (midnight) and also runs all the method through to 23:59, before rolling end to 00:00 again. We never ever write ‘24:00’. Friend will frequently see the moment in 24-hour clock created without a separator (‘.’ or ‘:’) between the hours and also minutes. For example 1400, which may be referred to as fourteen hundreds hours. This is especially common in military and also seafaring situations.

When making use of the 12-hour clock the 24 hour duration is separated into 2 12-hour periods. Both midnight and also midday are 12:00. Time before midday (noon) is designatedam(ante meridiem) and also time ~ noon is referred to aspm(post meridiem). Because that example, 4:10pm is the very same time together 16:10. Note that we never ever write ‘16:10pm’ The use of am and pm is only for the 12-hour clock.

You can also describe time in words, such together "ten minute past/after twelve", or "ten previous twelve". Increase to fifty percent way through an hour, we explain ‘minutes past’ the hour; past ‘half past’ we talk around minutes to/before the next hour. A time ‘on the hour’, for example 2:00pm, deserve to be described as ‘two pm’, ‘fourteen hundred’, or ‘two o’clock’.

Calculations of just how Much Time has actually Passed

You may need to do calculations of just how much time has passed, because that example, to work out the end time of an examination, just how long you will need to wait because that a train, or possibly to calculate gyeongju results.

If time is defined in words, girlfriend will require to transform it right into a digital form in order to do any type of calculations.

It is also simpler to usage the 24 hour clock to avoid any kind of confusion, uneven all your figures are one of two people am or pm.


Calculating the i of Time

In the normal way of things, to calculate exactly how much one thing is better than an additional you would simply subtract one native another. However, individually time is complicated because it’s no decimal. Instead of the columns being hundreds, tens and also units, they space hours, minutes and seconds.

Top Tip

If you have a scientific digital calculator, you will almost certainly have actually a button that will certainly calculate time. Technically, it’s for degrees yet as there space 60 minutes in a degree, and 60 secs in a minute, you can also use that to calculation time.

The switch will have actually a symbol favor this:


At the an extremely least, friend should be able to use that to convert time to decimals and ago again, make calculations much easier.

The other way of calculating how much time has passed in between Time A and Time B is:

work-related out how countless minutes from Time A come the next hour (or minute, if in minutes and also seconds). Job-related out how many hours between that following hour, and the last entirety hour prior to Time B. Occupational out how plenty of minutes indigenous the totality hour till time B. Add these 3 numbers together.

Worked Examples

Pat to be due to catch a train in ~ 11.44am, i m sorry she has actually just missed. The following train is not until 1.17pm. How long will certainly she need to wait?

Before girlfriend start, transform all the number to 24-hour clock because that ease. 11.44am i do not care 1144 and 1.17pm i do not care 1317.

The variety of minutes from 11:44 to 12:00 (the following hour) is 16. The number of hours from 12:00 to 13:00 is one. The variety of minutes native 13:00 to 13:17 is 17.

The full time that Pat will need to wait is 1 hour to add (16 + 17) minute = 1 hour 33 minutes.

I to be organising a series of canoe races, and have synchronised clocks because that the start and also the finish. The arrangement is for the first race to begin at around 30 minutes after synchronisation, climate four an ext races to begin at 2-minute intervals after ~ that, however it never ever works exactly. The starter keeps a document of the exact times, and also it turns out the on this occasion, races started at 28:02, 30:00, 32:15, 34:40 and 37:00.

The end up line has a clock, i beg your pardon is precisely synchronised through the start clock, and the finisher records the time top top the clock once the racers cross the end up line.

For every of the following finish times, work out just how long the contender took (click top top the + icons to view the working and answers):

Calculating the full amount that time spent

Sometimes you might need to add up how much time you have actually spent on a task that you have completed over several days or sessions. Including a list of hours and also minutes isn’t as straightforward as doing a normal enhancement calculation, due to the fact that (as above) we room not working with a decimal system.

For example, you may be law a gardening task for a neighbour, who has actually agreed to pay you an hourly rate of £10 every hour. ~ above the an initial day you invest 3 hours and 25 minute on the task, on the 2nd day you spend 2 hours and also 50 minutes and on the third day you finish it off in an hour and a quarter.

You need to add together the three amounts of time 3:25, 2:50 and 1:15. The an initial step is to add together every one of the minutes: 25 + 50 + 15 = 90 minutes. If you have to remind yourself exactly how to do an enhancement calculation, have a look at our page on addition.

As there are just 60 minutes in an hour, the next step is to convert 90 minutes into hours and also minutes:

90 ÷ 60 = 1.5 hours

The prize is a decimal, so us can convert it back into hours and minutes. You have the right to use a clinical calculator with a degrees duty as described above, or you have the right to do a bit more maths.

We can convert 0.5 hours into minutes.

0.5 × 60 = 30

1.5 hrs is thus 1 hour and also 30 minutes.

Next we require to include together the whole hours we have actually spent, which to be 3 top top the an initial day, 2 ~ above the second day and also 1 ~ above the third day: 3 + 2 + 1 = 6 hours.

Add the total hours to the complete minutes (in hours and minutes):

6h + 1h 30m = 7 hours and 30 minutes, or 7:30 spent gardening. In decimal form, this is 7.5 hours.

In order come calculate how much you have earned, we multiply the time (in decimals) by the hourly rate:

7.5 × 10 = 75. Friend have therefore earned $75.

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The most essential thing once calculating with time is to examine whether the answer looks around right?

If your 2 numbers are less than an hour apart, is her answer less than one hour? If lock are around 2 hrs apart as soon as you look in ~ them, is your answer? If not, friend may have lost or acquired some time somewhere!

If you want to know an ext about ‘about right’ take it a look at our page on Estimation, Approximation and also Rounding.