# 4th Class Mathematics Time and Calendar Time

Time

Category : 4th Class

Time

Synopsis

• 4 Time is measured using a clock.
• A clock has two hand, a long hand and a short hand. The long hand is called minute hand and the short hand is called hour hand.
• Some clocks have a third hand called second hand. Generally second hand is the thinnest hand. It moves much faster than the other two hands.

Some Conversions:

• hour $=\text{6}0$ minutes; 1 minute $=\text{6}0$ seconds

$\therefore$ 1 hour $=\text{6}0\times \text{6}0=\text{36}00$ seconds; 1 day $=\text{24}$ hours; 7 days $=\text{1}$ week;

12 months $=\text{1}$ year; 10 years $=\text{1}$ decade; 10 decades$=\text{1}$ century

$\therefore$ 100 years = 1 century

Time Notations:

• The time 12 o'clock in the midnight is written as 12 midnight. The time 12 o'clock in the noon is written as 12 noon.
• The time from 12 midnight to 12 noon is noted as a.m. (ante meridiem) and the time from 12 noon to 12 midnight as p.m. (post meridiem).
• In a 24 hour clock, the hours from each midnight to the next one are numbered from 0 to 24.
• Railway and airlines time tables are based on 24 hour clock.
• We write the 24 hour time in 4 digits. The first two digits represent hours and the last two digits represent minutes.

e.g., 14:20 hours

Time Calculations:

• 12 midnight is written as 24: 00 hours or 00: 00 hours. 12 noon is written as 12:00 hours.
• When we change p.m.to 24 hour clock time we add 12 to the hours and then write hours and minutes together without separating them.
• If the first two digits of 24 hour clock time show more than 12, the time will be in p.m. of 12 hour clock. To get time hours in p.m., we subtract 12 from first two digits.

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