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| Exercise 1.1

Question 2

Find the LCM and HCF of the following pairs of integers and verify that LCM×HCF=product of the two numbers\text{LCM} \times \text{HCF} = \text{product of the two numbers}.

(i) 2626 and 9191

(ii) 510510 and 9292

(iii) 336336 and 5454

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UNDERSTAND THE QUESTION

The question asks to find the Least Common Multiple (LCM) and Highest Common Factor (HCF) for three pairs of integers. It also requires verifying the fundamental property of number theory that for any two positive integers aa and bb, the product of their LCM and HCF is equal to the product of the numbers themselves (LCM(a,b)×HCF(a,b)=a×b\text{LCM}(a,b) \times \text{HCF}(a,b) = a \times b). The core concepts required are prime factorization, identifying common factors, and basic arithmetic multiplication.

PART I

Find the LCM and HCF of 26 and 91 and verify that LCM × HCF = product of the two numbers.

STEP 1PRIME FACTORIZATION OF THE NUMBERS

First, we determine the prime factorization of each number. For 2626:

26=2×13 26 = 2 \times 13 

For 9191:

91=7×13 91 = 7 \times 13 

STEP 2CALCULATE THE HCF

The HCF (or GCD) is the product of the lowest power of common prime factors. The common prime factor between 2626 and 9191 is 1313.

HCF(26,91)=13 \text{HCF}(26, 91) = 13 

STEP 3CALCULATE THE LCM

The LCM is the product of the highest power of all prime factors involved. The prime factors are 2,7,132, 7, 13.

LCM(26,91)=2×7×13=182 \text{LCM}(26, 91) = 2 \times 7 \times 13 = 182 

STEP 4VERIFY THE PROPERTY

We verify that LCM×HCF=Product of the two numbers\text{LCM} \times \text{HCF} = \text{Product of the two numbers}. Left Hand Side (LHS):

LCM×HCF=182×13=2366 \text{LCM} \times \text{HCF} = 182 \times 13 = 2366 

Right Hand Side (RHS):

26×91=2366 26 \times 91 = 2366 

Since LHS = RHS, the property is verified.

ANSWER

HCF = 13, LCM = 182. Verification: 182×13=2366182 \times 13 = 2366 and 26×91=236626 \times 91 = 2366.

PART II

Find the LCM and HCF of 510 and 92 and verify that LCM × HCF = product of the two numbers.

STEP 1PRIME FACTORIZATION OF THE NUMBERS

First, we determine the prime factorization of each number. For 510510:

510=10×51=2×5×3×17=2×3×5×17 510 = 10 \times 51 = 2 \times 5 \times 3 \times 17 = 2 \times 3 \times 5 \times 17 

For 9292:

92=4×23=22×23 92 = 4 \times 23 = 2^2 \times 23 

STEP 2CALCULATE THE HCF

The HCF is the product of the lowest power of common prime factors. The only common prime factor is 22. The lowest power is 212^1.

HCF(510,92)=2 \text{HCF}(510, 92) = 2 

STEP 3CALCULATE THE LCM

The LCM is the product of the highest power of all prime factors involved. The prime factors are 2,3,5,17,232, 3, 5, 17, 23. Highest powers: 22,31,51,171,2312^2, 3^1, 5^1, 17^1, 23^1.

LCM(510,92)=22×3×5×17×23 \text{LCM}(510, 92) = 2^2 \times 3 \times 5 \times 17 \times 23 
LCM(510,92)=4×3×5×17×23=60×391=23460 \text{LCM}(510, 92) = 4 \times 3 \times 5 \times 17 \times 23 = 60 \times 391 = 23460 

STEP 4VERIFY THE PROPERTY

We verify that LCM×HCF=Product of the two numbers\text{LCM} \times \text{HCF} = \text{Product of the two numbers}. Left Hand Side (LHS):

LCM×HCF=23460×2=46920 \text{LCM} \times \text{HCF} = 23460 \times 2 = 46920 

Right Hand Side (RHS):

510×92=46920 510 \times 92 = 46920 

Since LHS = RHS, the property is verified.

ANSWER

HCF = 2, LCM = 23460. Verification: 23460×2=4692023460 \times 2 = 46920 and 510×92=46920510 \times 92 = 46920.

PART III

Find the LCM and HCF of 336 and 54 and verify that LCM × HCF = product of the two numbers.

STEP 1PRIME FACTORIZATION OF THE NUMBERS

First, we determine the prime factorization of each number. For 336336:

336=2×168=22×84=23×42=24×21=24×3×7 336 = 2 \times 168 = 2^2 \times 84 = 2^3 \times 42 = 2^4 \times 21 = 2^4 \times 3 \times 7 

For 5454:

54=2×27=2×33 54 = 2 \times 27 = 2 \times 3^3 

STEP 2CALCULATE THE HCF

The HCF is the product of the lowest power of common prime factors. The common prime factors are 22 and 33. Lowest power of 22 is 212^1. Lowest power of 33 is 313^1.

HCF(336,54)=21×31=6 \text{HCF}(336, 54) = 2^1 \times 3^1 = 6 

STEP 3CALCULATE THE LCM

The LCM is the product of the highest power of all prime factors involved. The prime factors are 2,3,72, 3, 7. Highest powers: 24,33,712^4, 3^3, 7^1.

LCM(336,54)=24×33×7 \text{LCM}(336, 54) = 2^4 \times 3^3 \times 7 
LCM(336,54)=16×27×7=432×7=3024 \text{LCM}(336, 54) = 16 \times 27 \times 7 = 432 \times 7 = 3024 

STEP 4VERIFY THE PROPERTY

We verify that LCM×HCF=Product of the two numbers\text{LCM} \times \text{HCF} = \text{Product of the two numbers}. Left Hand Side (LHS):

LCM×HCF=3024×6=18144 \text{LCM} \times \text{HCF} = 3024 \times 6 = 18144 

Right Hand Side (RHS):

336×54=18144 336 \times 54 = 18144 

Since LHS = RHS, the property is verified.

OVERALL FINAL ANSWER

(i) HCF = 13, LCM = 182. Verification: 182×13=2366182 \times 13 = 2366 and 26×91=236626 \times 91 = 2366.
(ii) HCF = 2, LCM = 23460. Verification: 23460×2=4692023460 \times 2 = 46920 and 510×92=46920510 \times 92 = 46920.