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Tick-Tick-Tick - 24-hour Clock Format

Grade 4CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The 24-hour clock format is a way of telling time where the day runs from midnight to midnight and is divided into 2424 hours. Unlike the 12-hour clock, it does not use 'a.m.' or 'p.m.'. Imagine a long number line starting at 00 (midnight) and ending at 2424 (the next midnight).

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In this format, time is expressed using four digits: the first two digits represent the hours and the last two digits represent the minutes. For example, 08:2008:20 means 88 hours and 2020 minutes. Visualise a digital clock display where the hours always show two digits, like 05:0005:00 instead of just 55.

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Midnight is the start of the day and is written as 00:0000:00 hours. Noon is written as 12:0012:00 hours. If you look at a 24-hour clock face, you might see 1212 at the top, and as you move past it into the afternoon, the numbers continue as 13,14,15,13, 14, 15, and so on.

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For any time from 1:001:00 a.m. to 12:5912:59 p.m., the hours in the 24-hour format stay the same as the 12-hour format (except midnight). For example, 9:309:30 a.m. becomes 09:3009:30 hours. You can think of this as simply adding a leading zero if the hour is a single digit.

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To convert P.M. time (from 1:001:00 p.m. to 11:5911:59 p.m.) to the 24-hour format, you add 1212 to the number of hours. For example, to find 4:004:00 p.m. on a 24-hour scale, you take 44 and add 1212 to get 16:0016:00 hours. This is like continuing the count after 1212 noon (12+1=1312 + 1 = 13, 12+2=1412 + 2 = 14, etc.).

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To convert a 24-hour time back to a 12-hour P.M. time, if the hour is greater than 1212, you subtract 1212 from the hours and add 'p.m.'. If the time is 20:0020:00, you calculate 20−12=820 - 12 = 8, so it is 8:008:00 p.m.

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The 24-hour format is commonly used by railways, airlines, and the military to avoid confusion between day and night. Visualise a railway timetable where a train departing at 21:3021:30 clearly means 9:309:30 at night, leaving no doubt for the passengers.

📐Formulae

Time in 24-hour format (for P.M.)=(Hours in 12-hour format+12):Minutes\text{Time in 24-hour format (for P.M.)} = (\text{Hours in 12-hour format} + 12) : \text{Minutes}

Time in 12-hour format (if Hours >12)=(Hours in 24-hour format−12):Minutes P.M.\text{Time in 12-hour format (if Hours } > 12\text{)} = (\text{Hours in 24-hour format} - 12) : \text{Minutes P.M.}

12:00 Midnight=00:00 hours or 24:00 hours\text{12:00 Midnight} = 00:00 \text{ hours or } 24:00 \text{ hours}

12:00 Noon=12:00 hours\text{12:00 Noon} = 12:00 \text{ hours}

💡Examples

Problem 1:

Convert 5:255:25 p.m. into the 24-hour clock format.

Solution:

Step 1: Identify if the time is a.m. or p.m. Here, it is p.m. Step 2: Add 1212 to the hours. 5+12=175 + 12 = 17 Step 3: Keep the minutes the same (2525). Step 4: Combine them in HH:MMHH:MM format. The time is 17:2517:25 hours.

Explanation:

Since the time is in the evening (p.m.), we add 1212 to the hour to find its position in the 24-hour cycle.

Problem 2:

A train arrives at the station at 22:1022:10 hours. What is this time in the 12-hour clock format?

Solution:

Step 1: Check if the hours are greater than 1212. Here, 22>1222 > 12. Step 2: Subtract 1212 from the hours. 22−12=1022 - 12 = 10 Step 3: Keep the minutes the same (1010). Step 4: Since the original hours were more than 1212, we add 'p.m.' to the result. The time is 10:1010:10 p.m.

Explanation:

When the 24-hour clock shows a number greater than 1212, it represents a time in the afternoon or evening. Subtracting 1212 gives the equivalent 12-hour time.