Page 26 - SM inner class 7.cdr

E xercise 3.1

1. Sim plify the fol low ing.
(a) 6.25+2.3+ 2.635 (b) 0.236+2.3+520.2 (c) 26.35 – 2.1
(d) 1.1 – 0.011 (e) 25.20 + 94.38 - 45.99 (f) 11.6078 - 0.67 + 0.5
(g) 11.002 -2.36 – 4.965 – 7.9
2. What must be added to 19.63 to ob tain 57.87?

3. What must be sub tracted from 381.6 to ob tain 28.88?

Multiplication of Decimals And this shows : One decimal place of
1. Dec i mal is mul ti plied by a whole num ber mul ti pli cand + one dec i mal place of mul ti plier
= two dec i mal places of product
Step 1 : Mul ti ply the dec i mal with out the
dec i mal point with the given whole num ber. Let’s try few more examples:
.
.
.
´
Step 2 : Mark the dec i mal point in the prod uct 901 23 = 20723
=
.
.
.
´
to have as many places dec i mal as are there in 1634 141 230394
the given dec i mal. 3. When a dec i mal is mul ti plied by 1 :
For ex am ple : Mul ti ply 2.8 with 12 and we get When a decimal is multiplied by 1, the product
.
.
28 12 = 336 is equals to the given decimal itself.
´
Now you can notice that: Let’s try following examples to understand
Product 33.6 has one decimal place i.e. before this:
digit 6 011 1 011
´
.
=
.
and given decimal 2.8 also has one decimal 56 1 56
´
.
=
.
place i e. . before digit 8
4. Prod uct of a dec i mal and zero : Prod uct
Let’s try few more examples: of a dec i mal and zero re sults in zero it self.
.
237 ´ 34 = 26838 (Both Product and given Let’s try following examples to understand
.
decimals have one decimal places) this:
4 97 ´ 54 = 26838 (Both Product and given 25.03 ´ 0 = 0
.
.
decimals have two decimal places)
0 ´ 0.12 = 0
2. A decimal is multiplied by another
dec i mal Multiplication of a Decimal by 10, 100,
1000 etc :
Step 1 : Mul ti ply the two dec i mals with out the
dec i mal point just-like whole num bers. To multiply a decimal number with 10, 100,
1000, 10000 etc. count the number of zeroes
Step 2 : Mark the dec i mal point in the prod uct
following 1 in the multiplier and shift the
in such a way that the number of decimal
decimal point of the multiplicand towards
places in the prod uct is equal to the sum of the right for the places equal to the above count.
dec i mal places in the given dec i mals.
For ex am ple : 41827 100. ´ = 41827
.
For ex am ple : Mul ti ply 4.9 with 1.8 and we get
4.9 1.8 = 8.82 [dot moved 2 place right]
´
.
Similarly. 27704. ´ 10 = 27704
Now you can notice that:
´
and 624662 1000 = 624662
.
.
Product 8.82 has two decimal place i e. . digit 8
and 2 Division of Decimal
Multiplicand 4.9 has one decimal place i e. . 1. Di vi sion of dec i mal by a whole num ber
digit 9 For example : Di vide 0.135 by 5 :
Multiplier 1.8 has one decimal place i e. . digit 8 = 0.135 ÷ 5
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Mathematics In Focus - 7