Page 25 - SM inner class 7.cdr

+ 4 % 1 ¼ 3 ÷ ¾
×
Chapter3 6 ½ –

Decimals

Introduction Ex am ple 1. Cal cu late 5.84 + 8 + 12.79.
Decimals, also known as Decimal Fractions, So lu tion :
are the one in which Fractional Part, and 5. 84
8. 00
Whole Number Part are separated by a
+. 1 2 .7 9
DOT. 1 1 1
Whole Number Part Fractional Part 26 . 63
4 . 25
Note : The dec i mal point in the an swer is lined up
with the dec i mal points in the num bers set out
ver ti cally.
DOT

4.25, 989.101, 8873.9, 345.12 all are the Subtraction of Decimals
examples of a Decimal. To subtract a small decimal number from a
The number of digits contained in the decimal larger decimal number, write the small
number down with the larger one on top and
part of a decimal number is known as the
the decimal points underneath one another.
number of decimal places.
Then calculate the subtraction as you would
For ex am ple : 4.68 has two decimal places for whole numbers and line up the decimal
and 1111.111 has three dec i mal places. point in the an swer.
Ex am ple 2. Re write 3.67 – 1.83 in col umns and
.
e g. 1111111
.
then cal cu late.
So the place values for 1111.111 will be as:
So lu tion :
Digit 1st = 1000 i e. . thousands 2 3 . 67 3 . 67
1
1
Digit 2nd = 1000 ÷ 10 = 100 i.e. hundreds –1 . 83 or –1 1 . 83
1 . 84 1 . 84
Digit 3rd = 100 ÷ 10 = 10 i.e. tens
Ex am ple 3. Re write 83.47 – 57.684 in col umns
Digit 4th = 10 ÷ 10 = 1 i.e. ones and then cal cu late.
1
Digit 5th = ¸1 10 = i e. . tenths So lu tion :
10 7 8 3 . 4 7 0 8 3 . 4 7 0
1
1
12
13
1
16
1
1
1 1
Digit 6th = ¸ 10 = i e. hundredths – 5 7 . 6 8 4 or – 5 7 . 6 8 4
.
1
1
1
1
10 100 2 5 . 7 8 6 2 5 . 7 8 6
1 1 1
Digit 7th = ¸ = i e. thousandths Note : To add (or sub tract) dec i mals, al ways fill
.
100 10 1000
empty place val ues with ze ros so that all of the
Addition and Subtraction of Decimals num bers have the same num ber of dec i mal places.
Addition of Decimals Ex am ple 4. Re write 24 – 8.327 in col umns and
then cal cu late.
To add decimal numbers, insert zeros in empty
So lu tion :
decimal place values so that all of the numbers
1
1
1
13
1
9
1
9
1 2 4 . 0 0 0 2 4 . 0 0 0
have the same number of decimal places and
– 8 . 3 2 7 or – 8 . 3 2 7
write the numbers such that their decimal 1 1 1 1
1 5 . 6 7 3 1 5 . 6 7 3
points are below one another.
Note : 24 = 24.000
25
Mathematics In Focus - 7