Even otherwise highly numerate people have been known to throw up their hands in fear at the believed of including together times.

A mechanism like time, i m sorry is no decimal, can be counter-intuitive and also requires concentration.

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However, with a bit of application, girlfriend too can learn just how to calculate through time, and also gain to trust in manipulating hours, minutes and also seconds.

Basic units of Time

The straightforward units of time, which permit you to perform calculations entailing time, are:

Unit Notes
Second The 2nd is the worldwide System that Units (SI) measurement for time. The symbol "s" is offered to denote a second. Seconds are likewise commonly abbreviation to sec.
Minute 60 Seconds A minute nearly always has sixty seconds. However, really occasionally (approx. When every 18 months) a minute deserve to have 61 seconds. This "leap seconds" are supplied to keep our clocks aligned come the earth"s rotation around the sun.
Hour 60 Minutes It is typical to talk about "half one hour" (30 minutes) and "quarter of one hour" (15 minutes).
Day 24 hours
Week 7 days It is additionally common for people to talk about a occupational week, commonly 5 work (Monday - Friday) and weekends (Saturday and also Sunday).
Month 28,29, 30 or 31 days. Different months have different numbers of days. Every months have actually either 30 or 31 days other than for February. February has 28 days in a common year and an extra work in a leap year; the 29thday that February is called the leap day.
Year 12 Months A year constantly has 12 months. A year has approximately 52 weeks. A common year has actually 365 days and a leap year (occurring mainly every 4 years) has actually 366 days.
Decade 10 Years
Century 100 Years
Millennium 1,000 Years

Years room commonly break-up into quarters, particularly in business and also education settings, with each quarter being 3 months or around 90 days. Quarters in a details business or sector may not necessarily be the same as those suggested below:

The number of days in a month varies. All months have actually the same variety of days yearly except because that February which has 28 work 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 variety of days in a month varies, this also means that the variety of weeks in a month different too.

People often use approximations as soon as calculating the variety of days in months. For example, that is typical to usage the presumption that a month has four weeks, also though just February in a typical year actually does so.

This renders it tough to transform from months to weeks and also vice versa, unless you understand which months space being used, because there is no prompt ‘conversion factor’.

Top Tip!

If you space converting in between months and weeks, the best means to carry out so is via years, since they constantly contain 12 months (even in a leap year).

To convert months come weeks, division by 12 and also multiply by 52. To transform weeks to months, divide by 52 and also multiply through 12.

The answers you get will be an excellent approximations.

Writing Time

There are numerous different methods to write time. The easiest (digital) kind is as written hh.mm or hh:mm, for example 10.21 or 10:21.

Hours may be either split into 24 (known as the 24-hour clock) or two many 12 (often referred to as the 12-hour clock).

When utilizing the 24-hour clock, the 24 hour bicycle starts with the time 00:00 (midnight) and also runs every the method through to 23:59, prior to rolling end to 00:00 again. We never ever write ‘24:00’. Friend will often see the time in 24-hour clock created without a separator (‘.’ or ‘:’) in between the hours and also minutes. For example 1400, which may be described as fourteen hundreds hours. This is especially usual in military and seafaring situations.

When using the 12-hour clock the 24 hour duration is separated into 2 12-hour periods. Both midnight and also midday room 12:00. Time prior to midday (noon) is designatedam(ante meridiem) and time after noon is referred to aspm(post meridiem). For example, 4:10pm is the same time together 16:10. Keep in mind that we never ever write ‘16:10pm’ The use of am and pm is just for the 12-hour clock.

You can additionally describe time in words, such as "ten minutes past/after twelve", or "ten previous twelve". Increase to half way through an hour, we define ‘minutes past’ the hour; beyond ‘half past’ we talk about minutes to/before the following 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 how Much Time has actually Passed

You might need to perform calculations of just how much time has actually passed, for example, to occupational out the finish time of one examination, how long girlfriend will have to wait for a train, or perhaps to calculate race results.

If time is explained in words, you will require to convert it into a digital kind in order come do any kind of calculations.

It is likewise simpler to use the 24 hour clock come avoid any type of confusion, unless all your numbers are one of two people am or pm.


Calculating the passage of Time

In the normal method of things, to calculate just how much one thing is greater than another you would merely subtract one indigenous another. However, individually time is complex because it’s no decimal. Rather of the columns being hundreds, tens and also units, they room hours, minutes and also seconds.

Top Tip

If you have actually a scientific electronic calculator, girlfriend will almost certainly have actually a switch that will certainly calculate time. Technically, it’s because that degrees however as there are 60 minutes in a degree, and 60 secs in a minute, girlfriend can also use it to calculate time.

The switch will have a symbol favor this:


At the very least, you should be able to use that to transform time to decimals and earlier again, making calculations lot easier.

The other method of calculating how much time has actually passed between Time A and also Time B is:

occupational out how many minutes from Time A come the next hour (or minute, if in minutes and seconds). Work-related out how plenty of hours between that following hour, and the last whole hour prior to Time B. Occupational out how many minutes indigenous the totality hour until time B. Add these three numbers together.

Worked Examples

Pat to be due to capture a train at 11.44am, which she has actually just missed. The following train is not until 1.17pm. Just how long will she need to wait?

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

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

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

I to be organising a collection of canoe races, and have synchronised clocks for the start and the finish. The setup is because that the an initial race to start at around 30 minute after synchronisation, then four much more races to start at 2-minute intervals after that, but it never works exactly. The starter keeps a document of the specific times, and also it turns out the on this occasion, races began at 28:02, 30:00, 32:15, 34:40 and 37:00.

The finish line has actually a clock, i beg your pardon is precisely synchronised v the begin clock, and also the finisher records the time on the clock as soon as the racers overcome the complete line.

For each of the following complete times, work-related out exactly how long the contender took (click top top the + icons to view the working and also answers):

Calculating the complete amount of time spent

Sometimes you could need to add up just how much time you have actually spent ~ above a task that you have actually completed over number of days or sessions. Adding a perform of hours and also minutes isn’t together straightforward together doing a normal enhancement calculation, since (as above) we room not working through a decimal system.

For example, you may be act a gardening task for a neighbour, who has actually agreed to salary you one hourly price of £10 every hour. Top top the very first day you spend 3 hours and also 25 minutes on the task, top top the second day you invest 2 hours and 50 minutes and on the 3rd day you end up it turn off in an hour and a quarter.

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

As there are only 60 minutes in one hour, the following step is to convert 90 minutes into hours and minutes:

90 ÷ 60 = 1.5 hours

The price is a decimal, so us can transform it ago into hours and minutes. You have the right to use a clinical calculator with a degrees duty as explained above, or you have the right to do a bit much more maths.

We can convert 0.5 hrs into minutes.

0.5 × 60 = 30

1.5 hrs is as such 1 hour and 30 minutes.

Next we need to include together the totality hours we have spent, which to be 3 ~ above the an initial day, 2 ~ above the 2nd day and 1 on the third day: 3 + 2 + 1 = 6 hours.

Add the total hours come the total minutes (in hours and also minutes):

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

In order come calculate just how much you have actually earned, we multiply the moment (in decimals) through the hourly rate:

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

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The most necessary thing when calculating with time is to check whether the price looks about right?

If your 2 numbers are much less than an hour apart, is her answer much less than one hour? If lock are around 2 hours apart as soon as you look at them, is your answer? If not, you may have lost or got some time somewhere!

If you desire to know much more about ‘about right’ take it a look at our page on Estimation, Approximation and Rounding.