19. Measures-Length, Mass, Capacity, Measurement of Coins and Currency Notes

 

METRIC MEASURES

Learn and Remember:

        Metric system or decimal system of measurement is used to measure length, mass and capacity. Study the decimal places indicated in the following table :

 1.  Length:  In metric system, the methods of addition, subtraction, multiplication and division remain the same as in decimal fractions.

(i) Metre is the standard unit of length. mm, cm, km are the other units of length.

           1 cm = 10 mm, 1 m= 100 cm, 1 km = 1000 m.

(ii) Very small lengths, such as the thickness of a notebook, width of a coin, etc. are measured in millimetres. Centimetre is used for slightly bigger lengths.

(iii) Short distances are measured in metres.

(iv) Long distances are measured in kilometres.

 2. Mass :

(i) Gram is the standard unit of mass. mg and kg are the other units of mass.

1 kg = 1000 g, 100 kg = 1 quintal, 1 ton (metric) = 10 quintals.

(ii) Precious metals like gold and silver are measured in mg.

(iii) Cereals are measured in kg, quintal.

 3. Capacity :  The standard unit for capacity (volume) is litre.

11= 1000 ml, 1 m3 = 1000 litres, (1 mililitre = 1 centimetre 3)

Milk, kerosene, water, liquid medicines are measured in litres.

 4. Measurement of Time :

• 12-hour method of measurement of time :

(1) It is noon when a clock shows 12 o'clock.

(ii) The period from 12 o'clock (noon) to 12 o'clock (midnight) is post meridiem(pm).

(iii) The period from 12 o'clock (midnight) to 12 o'clock (noon) is ante meridiem(am).

Thus 8:25 am means 25 minutes past 8 in the morning.

5:45 pm means 45 minutes past 5 in the evening.

• 24-hour method of measurement of time :
• In this method 2 pm means 12+2 = 14:00.
• 9 pm means 12 +9=21:00
• 12  midnight means 24:00. This is shown as 00:00 hours. 17:30 means 30 minutes past 5 pm.
• 17 - 12=5).

1. Addition / Subtraction of hours and minutes :

(1) Addition : While adding the numbers showing hours and minutes, if the minutes add

up to more than 60, the minutes should be split up into hours and minutes. For example,

3 hours 47 minutes

4 hours 48 minutes

7 hours 95 minutes      

95 minutes = 1 hour 35 minutes. 

∴  7 hours 95 minutes

= 7 hours + 1 hour + 35 minutes

= 8 hours 35 minutes

(2) Subtraction : While subtracting the numbers showing hours and minutes, at times we have to borrow 1 hour. This hour that is 60 minutes are added to the given minutes and then the subtraction is carried out.

For example, 

(7 hours 10 min = 6 hours 70 min.)

7 hours 10 minutes – 2 hours 40 minutes.

Ans. 4 hours 30 minutes.

1. Measurement of Coins and Currency Notes :

Bigger coins and notes can be exchanged for smaller ones and vice-versa.

2. Dozen, gross, quire, ream:

1 dozen = 12 articles, 1 gross = 12 dozen, 1 gross = 144 articles,

1 quire = 24 pages, 1 ream = 20 quires, 1 ream = 480 pages.