Even otherwise extremely numerate people have been recognized to throw up your hands in fear at the assumed of adding together times.

A device like time, i m sorry is no decimal, have the right to be counter-intuitive and requires concentration.

You are watching: What is one half of 30

However, with a little bit of application, friend too have the right to learn just how to calculate v time, and also gain to trust in manipulating hours, minutes and also seconds.

Basic systems of Time

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

Unit Notes
Second The second is the global System that Units (SI) measurement because that time. The price "s" is offered to denote a second. Secs are likewise commonly abbreviation to sec.
Minute 60 Seconds A minute nearly always has sixty seconds. However, very occasionally (approx. Once every 18 months) a minute deserve to have 61 seconds. These "leap seconds" are offered to save our clocks aligned to the earth"s rotation around the sun.
Hour 60 Minutes It is typical to talk around "half an hour" (30 minutes) and "quarter of an hour" (15 minutes).
Day 24 hours
Week 7 days It is also common for civilization to talk around a occupational week, usually 5 days (Monday - Friday) and also weekends (Saturday and also Sunday).
Month 28,29, 30 or 31 days. Different month have various numbers of days. All months have actually either 30 or 31 days except for February. February has 28 work in a typical year and also 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 typical year has actually 365 days and also a leap year (occurring mainly every 4 years) has actually 366 days.
Decade 10 Years
Century 100 Years
Millennium 1,000 Years

Years are commonly split into quarters, particularly in business and education settings, with each quarter being 3 months or roughly 90 days. Quarters in a particular business or sector might not have to be the exact same as those indicated below:

The number of days in a month varies. All months have actually the same number of days every year except because that February which has 28 job 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 means that the number of weeks in a month varies too.

People regularly use approximations once calculating the variety of days in months. Because that example, the is typical to use the presumption that a month consists of four weeks, even though just February in a usual year in reality does so.

This renders it tough to transform from months to weeks and vice versa, unless you know which months room being used, since there is no immediate ‘conversion factor’.

Top Tip!

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

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

The answer you gain will be great approximations.

Writing Time

There are countless different means to write time. The most basic (digital) form is as written hh.mm or hh:mm, for example 10.21 or 10:21.

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

When using the 24-hour clock, the 24 hour cycle starts with the moment 00:00 (midnight) and also runs every the means through come 23:59, prior to rolling over to 00:00 again. We never write ‘24:00’. Girlfriend will regularly see the moment in 24-hour clock created without a separator (‘.’ or ‘:’) between the hours and minutes. For example 1400, which might be referred to as fourteen hundred hours. This is especially common in military and seafaring situations.

When making use of the 12-hour clock the 24 hour period is divided into 2 12-hour periods. Both midnight and midday are 12:00. Time prior to midday (noon) is designatedam(ante meridiem) and also time after ~ noon is referred to aspm(post meridiem). For example, 4:10pm is the very same time together 16:10. Keep in mind that we never 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 past twelve". Up to half way through an hour, we explain ‘minutes past’ the hour; beyond ‘half past’ us talk around minutes to/before the following hour. A time ‘on the hour’, for instance 2:00pm, can be referred to as ‘two pm’, ‘fourteen hundred’, or ‘two o’clock’.

Calculations of exactly how Much Time has Passed

You may need to carry out calculations of how much time has actually passed, for example, to work out the end time of an examination, just how long girlfriend will have to wait for a train, or maybe to calculate gyeongju results.

If time is defined in words, friend will need to transform it into a digital kind in order to do any calculations.

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


Calculating the i of Time

In the normal method of things, come calculate exactly how much one point is higher than an additional you would just subtract one native another. However, individually time is complex because it’s not decimal. Instead of the columns gift hundreds, tens and units, they space hours, minutes and also seconds.

Top Tip

If you have a scientific digital calculator, friend will practically certainly have a button that will calculate time. Technically, it’s for degrees yet as there room 60 minute in a degree, and 60 secs in a minute, girlfriend can also use that to calculate time.

The switch will have actually a symbol choose this:


At the really least, girlfriend should have the ability to use that to transform time to decimal and back again, do calculations lot easier.

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

occupational out how many minutes indigenous Time A to the next hour (or minute, if in minutes and also seconds). Work-related out how numerous hours between that next hour, and the last totality hour prior to Time B. Occupational out how many minutes from the whole hour till time B. Include these 3 numbers together.

Worked Examples

Pat to be due to catch a train in ~ 11.44am, which she has actually just missed. The following train is not till 1.17pm. How long will certainly she have to wait?

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

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

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

I am organising a collection of canoe races, and also have synchronised clocks for the start and the finish. The arrangement is for the very first race to start at around 30 minute after synchronisation, then four much more races to start at 2-minute intervals ~ that, however it never ever works exactly. The starter keeps a document of the precise times, and also it transforms out the on this occasion, races started at 28:02, 30:00, 32:15, 34:40 and 37:00.

The end up line has actually a clock, i m sorry is exactly synchronised through the begin clock, and also the finisher documents the time on the clock as soon as the racers overcome the complete line.

For every of the following complete times, work out how long the competitor took (click on the + icons to view the working and also answers):

Calculating the full amount of time spent

Sometimes you might need to include up just how much time you have spent top top a task that you have completed over number of days or sessions. Adding a perform of hours and minutes isn’t as straightforward as doing a normal addition calculation, because (as above) we are not working through a decimal system.

For example, you might be doing a gardening task for a neighbour, who has agreed to salary you one hourly rate of £10 per hour. On the first day you invest 3 hours and 25 minutes on the task, top top the 2nd day you spend 2 hours and also 50 minutes and also on the third day you finish it turn off in an hour and also a quarter.

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

As over there are only 60 minute in one hour, the next step is to transform 90 minutes into hours and also minutes:

90 ÷ 60 = 1.5 hours

The prize is a decimal, so us can convert it earlier into hours and minutes. You can use a clinical calculator v a degrees role as described above, or you deserve to do a bit an ext maths.

We can transform 0.5 hrs into minutes.

0.5 × 60 = 30

1.5 hours is because of this 1 hour and also 30 minutes.

Next we require to include together the entirety hours we have actually spent, which was 3 ~ above the very first day, 2 top top the 2nd day and also 1 on the third day: 3 + 2 + 1 = 6 hours.

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

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

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

7.5 × 10 = 75. Friend have because of this earned $75.

See more: How Far Is It From Daytona Florida To Orlando Florida ? Distance From Daytona Beach, Fl To Orlando, Fl


The most vital thing when calculating v time is to check whether the answer looks about right?

If your 2 numbers are much less than an hour apart, is your answer much less than one hour? If they are around 2 hrs apart once you look in ~ them, is her answer? If not, girlfriend may have lost or obtained some time somewhere!

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