model 5 lcm & hcf vs ratios Practice Questions Answers Test with Solutions & More Shortcuts

Question : 6 [SSC CGL 2010]

Two numbers are in the ratio 3 : 4. Their L.C.M. is 84. The greater number is

a) 28

b) 21

c) 24

d) 84

Answer: (a)

Let the numbers be 3x and 4x.

∴ Their LCM = 12x

∴ 12x = 84

⇒ x = $84/12$ = 7

∴ Larger number = 4x = 4 × 7 = 28

Question : 7 [SSC DEO 2009]

Two numbers are in the ratio 3 : 4. The product of their H.C.F. and L.C.M. is 2028. The sum of the numbers is

a) 86

b) 68

c) 72

d) 91

Answer: (d)

Using Rule 1,

1st number × 2nd number = L.C.M. × H.C.F

Let the numbers be 3x and 4x respectively

First number × second number

= HCF × LCM

⇒ 3x × 4x = 2028

⇒ $x^2 = 2028/{3×4}$ = 169

∴ x = $√{169}$ = 13

∴ Sum of the numbers

= 3x + 4x = 7x = 7 × 13 = 91

Question : 8

If the ratio of two numbers is 2 : 3 and their L.C.M. is 54, then the sum of the two numbers is

a) 45

b) 5

c) 15

d) 270

Answer: (a)

Let the two numbers are 2x and 3x respectively.

According to question,

LCM = 54

x (3×2)= 54

⇒ x = 9

Numbers = 2x = 2 × 9 = 18

and, 3x = 3 × 9 = 27

Sum of the two numbers

= 18 + 27 = 45

Question : 9 [SSC CGL 2011]

The ratio of the sum to the LCM of two natural numbers is 7 : 12. If their HCF is 4, then the smaller number is :

a) 12

b) 20

c) 16

d) 8

Answer: (a)

Let the numbers be 4x and 4y

where x and y are prime to each other.

LCM = 4xy

∴ $(\text"4x+4y")/ \text"4xy"$ = $7/12$

⇒ 12 (x + y) = 7 xy

⇒ x = 3, y = 4

∴ Smaller number = 4 × 3 = 12

Question : 10 [SSC MTS 2013]

Two numbers are in the ratio 3 : 4. If their HCF is 4, then their LCM is

a) 36

b) 48

c) 42

d) 24

Answer: (b)

Numbers = 3x and 4x

HCF = x = 4

∴ LCM = 12x = 12 × 4 = 48

IMPORTANT quantitative aptitude EXERCISES

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