# Hour

## What Is the Definition of an Hour?

An hour is one of the 24 equal parts of a day.

1 hour $= 60$ minutes

$= 3600$ seconds

Using the abbreviation of an hour, minutes, and seconds, we can write the above expression as:

1 h (or hr) $= 60$ min $= 3600$ sec

Let’s understand the concept of an hour more clearly with the help of a clock.

The numbers and the movement of the hour hand and minute hand on clocks help us calculate hours and the time, as well.

For example: Calculate the number of hours that have passed from Clock A to Clock B.

In the image given above, by looking at the two clocksA and Bwe can tell that:

• The hour hand in clock A is at 3, and the minute hand is at 12. (The time is 3 o’clock)
• The hour hand in clock B is at 5, and the minute hand is at 12. (The time is 5 o’clock)

Now, to calculate the number of hours from clock A to B, we need to subtract the number of the hour hand in Clock A from the number of the hour hand in Clock B.

$5$ $–$ $3 = 2$

Thus, 2 hours have passed from Clock A to Clock B.

## How Many Hours Are in a Day?

24 hours make up a whole day.

Numerically, we can write this as:

1 day $= 24$ hours

$= 1440$ minutes

$= 86,400$ seconds

In ancient times, when artificial lighting didn’t exist, people counted hours from sunrise and considered the middle of the day as the sixth hour’s end.

The hours also varied in their length. These fluctuations occurred because changes in seasons and differences in location led to changes in the quantity of daylight and night hours.

It was only when artificial lighting and clocks were invented (which helped measure time accurately) that the practice of dividing days into equal-sized chunks based on the number of hours taken off.

## Fun Facts!

• 168 hours make up a week.
• 8760 hours make up a year.
• In the past, sometimes, some people started counting the hours from sunset.

## Conclusion

An hour is a unit of time that is equal to 60 minutes.

In ancient times, it varied in length due to changes in seasons. Since there were no clocks and artificial lighting available, people counted the hours from sunrise.

However, with the invention of timekeeping instruments, the scenario has changed. The number of hours no longer varies in length and remains fixed. Also, people keep track of time with the help of smart clocks and watches.

Knowing the concept of the hour thus helps in calculating time.

## Solved Examples

1. Sam has to leave for a meeting at 7 o’clock. Right now, it is 4 o’clock. How many hours are left before he has to leave?

Solution: To find the number of hours left for Sam to leave, we need to subtract 4 from 7.

$7$ $-$ $4 = 3$.

So, Sam has 3 hours left before he has to leave for the meeting.

2. Find the number of hours present in 330 minutes.

Solution: 1 hour $= 60$ minutes.

To find out the number of hours in 330 minutes, we need to divide 330 by 60.

$\frac{330}{60} = 5.5$

This means there are 5 and a half hours (or 5 hours and 30 minutes) in 330 minutes.

3. Ken has ordered sets of different cookies. They will get delivered in 2 hours. He is curious to know how many seconds there are in 2 hours. Help him out by finding the answer.

Solution: We know that 1 hour $= 3600$ seconds.

So, 2 hours $= 2 \times 3600 = 7200$ seconds.

Thus, there are 7200 seconds in 2 hours.

4. How many hours are there in 4 days?

Solution: We know that 1 day $= 24$ hours.

So, 4 days $= 4 \times 24 = 96$ hours.

This means that there are 96 hours in 4 days.

5. How many milliseconds are there in 1 hour? (Hint: 1 second $= 1000$ milliseconds)

Solution: 1 hour time $= 3600$ seconds.

To find the number of milliseconds in an hour, we need to multiply 1000 by 3600.

$1000 \times 3600 = 3600000$.

Thus, in 1 hour, there are 3,600,000 milliseconds.

## Practice Problems

1

### At 2 o’clock, Shelly put a preheated cake in the refrigerator. She plans to take it out at 8 o’clock. How many hours does she need to wait?

4 hours
6 hours
8 hours
10 hours
CorrectIncorrect
To find the number of hours, subtract 2 from 8.
$8$ $-$ $2 = 6$.
This means that Shelly needs to wait for 6 hours before she can take the cake out of the refrigerator.
2

### How many minutes are there in 10 hours?

200 minutes
300 minutes
500 minutes
600 minutes
CorrectIncorrect
60 minutes $= 1$ hour
To find the number of minutes in 10 hours, you need to multiply 60 by 10.
$60 \times 10 = 600$
Thus, there are 600 minutes in 10 hours.
3

### Lydia is planning to go on a trip for 6 days. Help her out by finding how many hours are present in 6 days.

124 hours
134 hours
144 hours
154 hours
CorrectIncorrect
1 day $= 24$ hours.
To find the number of hours in 6 days, we multiply 24 by 6.
$24 \times 6 = 144$.
Thus, 144 hours are present in 6 days.
4

### Find the correct option.

960 min $= 16$ hrs
950 min $= 16$ hrs
860 min $= 16$ hrs
850 min $= 16$ hrs
CorrectIncorrect
Correct answer is: 960 min $= 16$ hrs
1 hour $= 60$ minutes
16 hours $= 16 \times 60 = 960$ minutes
5

### In about 420 minutes, Brian can return home from his school. Find the number of hours present in 420 minutes.

5 hours
7 hours
9 hours
11 hours
CorrectIncorrect
Since 60 minutes = 1 hour
To find the number of hours in 420 minutes, you need to divide 420 by 60.
$\frac{420}{60} = 7$
This means that Brian can return home from his school in 7 hours.

What is a second? How many seconds are there in an hour?

A second is a primary unit of time.

$1 \text{hour} = 60$ minutes and 1 minute $= 60$ seconds

So $1 \text{hour} = 60 \times 60$ seconds $= 3600$ seconds

A minute is a unit of time that is equal to 60 seconds.

60 minutes makes an hour.

A month may have 30 or 31 days.

$1 \text{day} = 24$ hours

$30 \text{days} = 30 \times 24 = 720$

In a month of 30 days, there are 720 hours.

$31 \text{days} = 31 \times 24 = 744$

In a month of 31 days, there are 744 hours.

A common year has 365 days.

$1 \text{Day} = 24$ hours

So every common year has: $365 \times 24 = 8760$ hours

Every leap year has: $366 \times 24 = 8784$ hours

The earth completes one entire rotation in approximately 24 hours. Therefore, we experience one day and one night within 24 hours. That is why we have only twenty-four hours in a day.