Page 20 - SM inner class 7.cdr

3. Find the value of :
3 7 4 7 5
(a) of 75 kg (b) of ` 270 (c) of (d) of 1 year
5 18 9 24 6
5 2 5 7 1
(e) of 75 kg (f) of 180 degree (g) of (h) of 1day
6 9 14 15 6
4. Simplify the fol low ing :
1 2 1 1 1 1 1 3 5 5 1 1 1 5
(a) 3 ´ ´ 1 (b) 2 ´ 1 ´ 1 (c) 2 ´ 1 ´ 1 ´ (d) 5 ´ 4 - 3 ´ 1
3 5 14 3 2 6 7 46 18 7 3 2 4 6

Reciprocal of a Fraction Division of Fractions

To get the reciprocal of a fraction, just turn it 1. Di vi sion of Frac tion by Whole Num ber
up side down. Steps of division are:
In other words swap over the Numerator and Step 1 : Find re cip ro cal of given whole num ber
Denominator. Step2 : Mul ti ply given frac tion with re cip ro cal
For ex am ple: of given whole num ber (cal cu lated in step 1)
Fraction Reciprocal Step3: The mul ti pli ca tion of nu mer a tors,
di vided by, mul ti pli ca tion of de nom i na tors is
3 8
the re quired answer.
8 3
15
5 6 Ex am ple 16. Di vide by 10.
4
6 5
19 7 So lu tion : Write fraction and whole number
7 19 in di vi sion ex pres sion and we get:

1 2 15
= 2 ¸ 10
2 1 4
Note : When we multiply a frac tion by its Find the Reciprocal of whole number i.e. 10
re cip ro cal we get 1: 1
Reciprocal of 10 =
5 6 1
=
as ´ = 1 ´ 3 1 10
6 5 3 15
Multiply fraction with the reciprocal of
Ex am ple 14 : (a) Find the re cip ro cal of 20 4
3
(b) Find the reciprocal of whole number (calculated above) and we get;
7 æ15 ö æ 1 ö
1 = ç ÷ ´ ç ÷
So lu tion : (a) Re cip ro cal of 20 is . è 4 ø è10 ø
20
3 7 Multiplication of numerators, divided by,
(b) Reciprocal of =
7 3 multiplication of denominators and we get;
1
1 (15 ´ )
= 2 =
3 (4 ´10 )
1
Ex am ple 15 : Find the re cip ro cal of 1 Solve the Brackets and we get;
3 15
1 4 =
So lu tion : 1 = 40
3 3
15 15 3
1 3 Hence, ¸10 = =
\ Reciprocal of 1 is 4 40 8
3 4

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Mathematics In Focus - 7