model 1 Basic formula of LCM & HCF Practice Questions Answers Test with Solutions & More Shortcuts

Question : 6 [S.S.C. (CHSL) 2013]

The product of two numbers is 2160 and their HCF is 12. Number of such possible pairs is

a) 1

b) 2

c) 3

d) 4

Answer: (b)

HCF = 12

Numbers = 12x and 12y

where x and y are prime to each other.

∴ 12x × 12y = 2160

⇒ xy = $2160/{12 × 12} $

= 15 = 3 × 5, 1 × 15

Possible pairs = (36, 60) and (12, 180)

Hence , Number of such possible pairs is 2.

Question : 7 [S.S.C. (CGL) 2004]

The HCF of two numbers is 23 and the other two factors of their LCM are 13 and 14. The larger of the two numbers is :

a) 276

b) 299

c) 345

d) 322

Answer: (d)

HCF is 23. So the other two numbers would be,

(23 * 13) and (23 * 14).

Thus Larger Number = 23 * 14 = 322.

Question : 8 [S.S.C. (CGL) 1999]

LCM of two numbers is 225 and their HCF is 5. If one number is 25, the other number will be?

a) 5

b) 25

c) 45

d) 225

Answer: (c)

Given, LCM = 225, HCF = 5,

First Number = 25 , Second Number = ?

We can find the Second Number with the help of given formula,

"LCM × HCF = 1st Number× 2nd Number"

⇒ 225 × 5 = 25 × 2nd Number

2nd Number = ${\text"225 x 5"}/25$

∴ 2nd Number = 45

Question : 9 [S.S.C. (CHSL) 2011]

The H.C.F. of two numbers is 96 and their L.C.M. is 1296. If one of the number is 864, the other is

a) 132

b) 135

c) 140

d) 144

Answer: (d)

Using Rule 1 :

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

First number × Second number = HCF × LCM

⇒ 864 × Second number

= 96 × 1296 ⇒ Second number

${96 × 1296}/864$ = 144

Question : 10 [S.S.C. (CGL) 2011]

The HCF and LCM of two numbers are 12 and 924 respectively. Then the number of such pairs is

a) 0

b) 1

c) 2

d) 3

Answer: (c)

IMPORTANT quantitative aptitude EXERCISES

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