# 3rd Class Mathematics Time and Calendar Introduction

## Introduction

Category : 3rd Class

### Introduction

There are various unit by which the time can be denoted. The Sl unit (Standard International unit) of time is second. Hour and minute are calculated along with the Sl unit of time. The format of numbers that we use today for time is based on60. We know that 60 seconds is equal to 1 minute and 60 minutes is equal to 1hour. Calendar that we use today is actually adopted from Gregorien calendar. Calendar always starts from 1 January. If the year is exactly divisible by 4 then the year is called leap year and a leap year contains 29 days of February. The name ofthe months is based on Latin words.

Time indicating watch

Watch indicates time. The face of watch is called its dial. Dial of a watch is divided into twelve big divisions from 1 to 12. The gaps among the numbers are divided into five small divisions that indicates minutes. Therefore, one small division    indicates one minute and there are 60 small divisions between 1 and 12 which    indicate 60 minutes. Minutes of a watch are calculated by the rotation of minute hand and hour is calculated by rotation of the hour hand. Therefore, there are    three hands in a watch. The biggest hand of the watch is called its seconds indicating hand and the hand whose length is shorter than the seconds hand is called its minute hand and it indicates minutes. The smallest hand of the watch is called its hour hand.

In the above figure a watch is shown. The biggest hand is its seconds indicating hand. It moves faster as compare to the movement of other two hands. In the watch, the hour hand can be easily identified by its speed of rotation. Minute hand moves one small division on one complete rotation of the second hand. The second biggest hand of the arm is its minute hand and hour hand moves to one big division by one complete rotation of the minute hand. Therefore, if minute hand rotates one complete rotation then the hour hand moves from one big division of one hour to another big division of second hour.

Look at the following picture of division of minutes and hour in the watch:

Conversion of Time

One minute is equal to 60 seconds and one hour is equal to 60 minutes, therefore,one unit can be converted into another. 110 minutes is converted into hour as 60minutes + 50 minutes = 1 hour 50 minutes.

Time conversion table

 60 seconds (sec) 1 minute (min) 60 minutes 1 hour (hr) 24 hours 1 day 7 day 1 week 14 day 2 week 30 days 1 month 12 months 1 year 365 days 1 year

The time taken by a worker A to complete a work is 3 hours and 12 minutes. If another worker B takes 1 hour 4 minutes to complete the same work then time taken by a worker A is how many times of the time taken by the worker B.

(a) 3 times

(b) 2 times

(c) 4 times

(d) 6 times

(e) All of these

Explanation Time taken by the worker A is 3 hours 12 minutes =60 +60+60 +12 =192 minutes and time taken by worker B= 60 +4 =64. Therefore,the part of time taken by another worker  times

Ante Meridian (A.M) and Post Meridian (P.M)

A day is divided into two parts, day and night and there are 24 hours in a day. The time of a day is divided into two parts A.M and P.M. The time from 12 midnight to12 noon is denoted by A.M (Ante meridian). P.M (Post meridian) is used along with the time from 12 noon to 12 midnight. Therefore, A.M. and P.M. are the convenient method to express the part of the day. To express the part of the day in A.M. and P.M., put A.M. and P.M. along with the time.

A watch is indicating the time of 4 o'clock 35 minutes at night. If Mariam wants to record the time for long time as shown by the clock exactly at 4 o'clock 35 minutes then which one of the following must be written along with the date and time?

(a) P.M.

(b) A.M.

(c) Noon

(d) Midnight

(e) None of these

Exacerbation: The time shown by the clock in the night is 4 o'clock 35 minutes therefore, it is expressed by 4:35 (4 o'clock 35 minutes) A.M.

Operations on Time

The following steps are used for operations on time:

Step 1:   Convert the time from hours into seconds or minutes.

Step 2:   Do the required operations.

Step 3:   Express the results in required units.

Two man and two woman do the work in 12 days on working 6 hours 20 minutes in a day. Find the total working hours of all of them which is required to complete the work?

(a) 76 hours

(b) 62 hours

(c) 63 hours

(d) 64 hours

(e) None of these