RS Aggarwal solution class 8 chapter 1 Rational Numbers Exercise 1D

Exercise 1D

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Q1 | Ex-1D | Rational Numbers | Class 8 | RS AGGARWAL | Chapter 1 | myhelper

Question 1:

Find each of the following products:
(i) 35×-78
(ii) -92×54
(iii) -611×-53
(iv) -23×67
(v) -125×10-3
(vi) 25-9×3-10
(vii) 5-18×-920
(viii) -1315×-2526
(ix) 16-21×145
(x) -76×24
(xi) 724×-48
(xii) -135×-10

Answer 1:

(i)

35×-78=3×(-7)5×8=-2140

(ii)

-92×54=(-9)×52×4=-458

(iii)

-611×-53=(-6)×(-5)11×3=3033

Simplifying the above rational number, we get:

3033=30÷333÷3=1011

(iv)

-23×67=(-2)×63×7=-1221

Simplifying the above rational number, we get:

-1221=-12÷321÷3=-47

(v)

-125×10-3=(-12)×105×(-3)=-120-15=12015

Simplifying the above rational number, we get:

12015=120÷315÷3=405=8

(vi)

25-9×3-10=25×3(-9)×(-10)=7590

Simplifying the above rational number, we get:

7590=75÷1590÷15=56

(vii)

5-18×-920=5×(-9)-18×20=-45-360=45360

Simplifying the above rational number, we get:

45360=45÷45360÷45=18

(viii)

-1315×-2526=(-13)×(-25)15×26=325390

Simplifying the above rational number, we get:

325390=325÷5390÷5=6578=65÷1378÷13=56

(ix)

16-21×145=16×14(-21)×5=224-105

Simplifying the above rational number, we get:

224-105=224÷7(-105)÷7=32-15=32×-1-15×-1=-3215

(x)

-76×24=(-7)×246=-1686

Simplifying the above rational number, we get:

-1686=(-168)÷26÷2=843=-84÷33÷3=-28

(xi)

724×(-48)=7×(-48)24=-33624

Simplifying the above rational number, we get:

-33624=-336÷2424÷24=-14

(xii)

-135×(-10)=(-13)×(-10)5=1305

Simplifying the above rational number, we get:

1305=130÷55÷5=26


Q2 | Ex-1D | Rational Numbers | Class 8 | RS AGGARWAL | Chapter 1 | myhelper

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Question 2:

Verify each of the following:
(i) 37×-59=-59×37
(ii) -87×139=139×-87
(iii) -125×7-36=7-36×-125
(iv) -8×-1312=-1312×-8

Answer 2:

(i)

37×-59=-59×37

 LHS=3×(-5)7×9        =-1563Simplifying, we get:-1563=-15÷363÷3=-521

  RHS=-59×37=(-5)×39×7=-1563Simplifying, we get:=-15÷363÷3=-521

LHS = RHS


(ii)

$\frac{-8}{7} \times \frac{13}{9}=\frac{13}{9} \times \frac{-8}{7}$

LHS$=\frac{-8}{7} \times \frac{13}{9}=\frac{(-8) \times 13}{7 \times 9}=-\frac{104}{63}$

RHS$=\frac{13}{9} \times \frac{-8}{7}=\frac{13 \times(-8)}{9 \times 7}=-\frac{104}{63}$

LHS=RHS


(iii)

-125×7-36=7-36×-125

 LHS =-125×7-36=(-12)×75×(-36)=84180Simplifying, we get: =84÷12180÷12=715

 RHS=7-36×-125=7×(-12)(-36)×5=84180Simplifying, we get:=84÷12180÷12=715

LHS = RHS


(iv)
-8 ×-1312=-1312×(-8)

 LHS =-8 ×-1312=(-8)×(-13)12=10412Simplifying, we get: =104÷412÷4=263

RHS=-1312×(-8)=(-13)×(-8)12=10412Simplifying, we get: =104÷412÷4=263

LHS = RHS


Q3 | Ex-1D | Rational Numbers | Class 8 | RS AGGARWAL | Chapter 1 | myhelper

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Question 3:

Verify each of the following:
(i) 57×1213×718=57×1213×718
(ii) -1324×-125×3536=-1324×-125×3536
(iii) -95×-103×21-4=-95×-103×21-4

Answer 3:

(i)

57×1213×718=57×1213×718

LHS=57×1213×718=5×127×13×718=6091×718=4201638=1039


RHS=57×1213×718=57×12×713×18=57×84234=4201638=1039

∴ ​57×1213×718=57×1213×718


(ii)

-1324×-125×3536=-1324×-125×3536

 LHS=-1324×-125×3536=-1324×(-12)×355×36=-1324×-420180=54604320=9172


 RHS=-1324×-125×3536=(-13)×(-12)24×5×3536=156120×3536=156×35120×36=54604320=9172

 ∴ ​-1324×-125×3536=-1324×-125×3536


(iii)

-95×-103×21-4=-95×-103×21-4

  LHS=-95×-103×21-4=(-9)×(-10)5×3×21-4=9015×21-4=90×2115×(-4)=-189060=-632


  RHS=-95×-103×21-4=-95×(-10)×213×(-4)=-95×21012=(-9)×2105×12=-189060=-632

∴ (-95×-103)×21-4=-95×(-103×21-4)


Q4 | Ex-1D | Rational Numbers | Class 8 | RS AGGARWAL | Chapter 1 | myhelper

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Question 4:

Fill in the blanks:

(i) $\frac{-23}{17} \times \frac{18}{35}=\frac{18}{35} \times(\ldots \ldots)$

(ii) $-38 \times \frac{-7}{19}=\frac{-7}{19} \times(\ldots \ldots)$

(iii) $\left(\frac{15}{7} \times \frac{-21}{10}\right) \times \frac{-5}{6}=(\ldots \ldots) \times\left(\frac{-21}{10} \times \frac{-5}{6}\right)$

(iv) $\frac{-12}{5} \times\left(\frac{4}{15} \times \frac{25}{-16}\right)=\left(\frac{-12}{5} \times \frac{4}{15}\right) \times(\ldots \ldots)$

Answer 4:

(i) $\frac{-23}{17} \times \frac{18}{35}=\frac{18}{35} \times \boxed{\frac{-23}{17}}$ 

(a×b=b×a)

(ii) $-38 \times \frac{-7}{9}=\frac{-7}{9} \times \fbox{-38}$ 

(a×b=b×a)

(iii) $\left(\frac{15}{7} \times \frac{-21}{10}\right) \times \frac{-5}{6}=\boxed{\frac{15}{7}} \times\left(\frac{-21}{10} \times \frac{-5}{6}\right)$ 

[a×(b×c)=(a×b)×c)]

(iv) $\frac{-12}{5} \times\left(\frac{4}{15} \times \frac{25}{-16}\right)=\left(\frac{-12}{5} \times \frac{4}{15}\right) \times \boxed{\frac{25}{-16}}$ 

[∵a×(b×c)=(a×b)×c]


Q5 | Ex-1D | Rational Numbers | Class 8 | RS AGGARWAL | Chapter 1 | myhelper

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Question 5:

Find the multiplicative inverse (i.e., reciprocal) of:
(i) 1325
(ii) -1712
(iii) -724
(iv) 18
(v) −16
(vi) -3-5
(vii) −1
(viii) 02
(ix) 2-5
(x) -18

Answer 5:

(i) Reciprocal of $\frac{13}{25}$ is $\frac{25}{13}$

(ii) Reciprocal of $\frac{-17}{12}$ is $\frac{12}{-17}$, that is, $\frac{-12}{17}$.

(iii) Reciprocal of $\frac{-7}{24}$ is $\frac{24}{-7}$, that is, $\frac{-24}{7}$.

(iv) Reciprocal of 18 is $\frac{1}{18}$

(v) Reciprocal of -16 is $\frac{1}{-16}$, that is, $\frac{-1}{16}$.

(vi) Reciprocal of $\frac{-3}{-5}$ is $\frac{-5}{-3}$, that is, $\frac{5}{3}$

(vii) Reciprocal of-1 is -1.

(viii) Reciprocal of $\frac{0}{2}$ does not exist as $\frac{2}{0}=\infty$

(ix) Reciprocal of $\frac{2}{-5}$ is $\frac{-5}{2}$

(x) Reciprocal of $\frac{-1}{8}$ is -8.

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Q6 | Ex-1D | Rational Numbers | Class 8 | RS AGGARWAL | Chapter 1 | myhelper

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Question 6:

Find the value of:
(i) 58-1
(ii) -49-1
(iii) -7-1
(iv) 1-3-1

Answer 6:

We know that  a-1=1a or a-1×a=1

(i)58-1=85 58×58-1=1(ii)-49-1=9-4=-94-49×-49-1=1(iii)(-7)-1=1-7=-17-7×(-7)-1=1

(iv) (-3)-1(-3)-1=1-3=-13 (-3)-1×-3 = 1


Q7 | Ex-1D | Rational Numbers | Class 8 | RS AGGARWAL | Chapter 1 | myhelper

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Question 7:

Verify the following:
(i) 37×56+1213=37×56+37×1213
(ii) -154×37+-125=-154×37+-154×-125
(iii) -83+-1312×56=-83×56+-1312×56
(iv) -167×-89+-76=-167×-89+-167×-76

Answer 7:

 (i)LHS=37×56+1213=37×65 +7278=37×13778=137182RHS=37×56+1213×37=3×57×6+12×313×7=1542+3691=195+216546=411546=137182

∴ ​37×(56+1213)=(37×56)+(37×1213)

(ii)LHS=-154×(37+-125)=-154×(15-8435)=-154×-6935=(-15)×(-69)140=1035140=20728RHS=(-154×37)+(-154×-125)=(-15)×34×7+(-15)×(-12)4×5=-4528+18020=-225+1260140=1035140=20728 -154×(37+-125)=(-154×37)+(-154×-125)

(iii)

(-83+-1312)×56=(-83×56)+(-1312×56)LHS=(-83+-1312)×56=-32-1312×56=-4512×56=-45×512×6=-22572=-225÷972÷9=-258RHS=(-83×56)+(-1312×56)=-8×53×6+(-13)×512×6=-4018+-6572=-160-6572=-22572=-225÷972÷9=-258 (-83+-1312)×56=(-83×56)+(-1312×56)

(iv)

-167×(-89+-76)=(-167×-89)+(-167×-76)LHS=-167×(-89+-76)=-167×(-16-2118)=-167×-3718=592126=29663RHS=(-167×-89)+(-167×-76)=12863+11242=256+336126=592126=29663 -167×(-89+-76)=(-167×-89)+(-167×-76)


Q8 | Ex-1D | Rational Numbers | Class 8 | RS AGGARWAL | Chapter 1 | myhelper

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Question 8:

Name the property of multiplication illustrated by each of the following statements:
(i) -158×-127=-127×-158
(ii) -23×79×-95=-23×79×-95
(iii) -34×-56+78=-34×-56+-34×78
(iv) -169×1=1×-169=-169
(v) -1115×15-11=15-11×-1115=1
(vi) -75×0=0

Answer 8:

  1. Commutative property
  2. Associative property
  3. Distributive property
  4. Property of multiplicative identity
  5. Property of multiplicative inverse
  6. Multiplicative property of 0


Q9 | Ex-1D | Rational Numbers | Class 8 | RS AGGARWAL | Chapter 1 | myhelper

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Question 9:

Fill in the blanks:
(i) The product of a rational number and its reciprocal is .......
(ii) Zero has ....... reciprocal.
(iii) The numbers ....... and ....... are their own reciprocals.
(iv) zero is ....... the reciprocal of any number.
(v) The reciprocal of a, where a ≠ 0, is .......
(vi) The reciprocal of 1a, where a ≠ 0, is .......
(vii) The reciprocal of a positive rational rational number is .......
(viii) The reciprocal of a negative rational number is .......

Answer 9:

(i) 1
(ii) no
(iii) 1; -1
(iv) not
(v) 1a
(vi) a
(vii) positive
(viii) negative

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