# HCF and LCM Questions

Q:

A rectangular courtyard 3.78 meters long 5.25 meters wide is to be paved exactly with square  tiles, all of the same size. what is the largest size of the tile which could be used for the purpose?

 A) 14 cms B) 21 cms C) 42 cms D) None of these

Explanation:

3.78 meters =378 cm = 2 × 3 × 3 × 3 × 7

5.25 meters=525 cm = 5 × 5 × 3 × 7

Hence common factors are 3 and 7

Hence LCM = 3 × 7 = 21

Hence largest size of square tiles that can be paved exactly with square tiles is 21 cm.

58 12158
Q:

The greatest number which on dividing 1657 and 2037 leaves remainders 6 and 5 respectively, is:

 A) 123 B) 127 C) 235 D) 305

Explanation:

Required number = H.C.F. of (1657 - 6) and (2037 - 5)

= H.C.F. of 1651 and 2032 = 127.

58 12004
Q:

The product of two numbers is 2028 and their H.C.F. is 13. The number of such pairs is:

 A) 1 B) 2 C) 3 D) 4

Explanation:

Let the numbers 13a and 13b.

Then, 13a x 13b = 2028

=>ab = 12.

Now, the co-primes with product 12 are (1, 12) and (3, 4).

[Note: Two integers a and b are said to be coprime or relatively prime if they have no common positive factor other than 1 or, equivalently, if their greatest common divisor is 1 ]

So, the required numbers are (13 x 1, 13 x 12) and (13 x 3, 13 x 4).

Clearly, there are 2 such pairs.

21 11867
Q:

Product of two co-prime numbers is 117. Their L.C.M  should be

 A) 1 B) 117 C) Equal to their H.C.F D) cannot be calculated

Explanation:

H.C.F of co-prime numbers is 1. So, L.C.M = $\inline&space;\fn_jvn&space;\frac{117}{1}$ =117

28 10945
Q:

The sum of two numbers is 528 and their H.C.F is 33. The number of pairs of numbers satisfying the above condition is

 A) 4 B) 6 C) 8 D) 12

Explanation:

Let the required numbers be 33a and 33b.

Then 33a +33b= 528   $\inline&space;\fn_jvn&space;\Rightarrow$   a+b = 16.

Now, co-primes with sum 16 are (1,15) , (3,13) , (5,11) and (7,9).

$\inline&space;\fn_jvn&space;\therefore$ Required numbers are  ( 33 x 1, 33 x 15), (33 x 3, 33 x 13), (33 x 5, 33 x 11), (33 x 7, 33 x 9)

The number of such pairs is 4