Question
If the product of two positive integers is 144, which of the following could be the LCM and HCF of the two numbers?
I. LCM : 24; HCF : 6
II. LCM : 18; HCF : 8
III. LCM : 16; HCF : 9
A. I only
B. II and III only
C. I and II only
D. I and III only
E. I, II and III
Correct Answer : Choice A
Explanatory Answer
Result 1:
The product of two positive integers ‘a’ and ‘b’ is equal to the product of the LCM (a, b) and HCF (a, b).
i.e., a * b = LCM (a, b) * HCF (a, b)
Result 2:
HCF is a factor of both the positive integers.
LCM is a multiple of both the positive integers.
So, it is evident that the LCM of the two positive integers has to be a multiple of the HCF of the two numbers.
Combining these two results, we have to find out which among the pairs has a product of 144 such that the LCM is a multiple of the HCF.
I. LCM : 24 and HCF : 6. Product of the LCM and HCF = 24 * 6 = 144. The LCM 24 is a multiple of the HCF 6. Hence, this is a possible pair.
II. LCM : 18 and HCF : 8. Product of the LCM and HCF = 18 * 8 = 144. However, the LCM 18 is NOT a multiple of the HCF 8. Hence, this one is not a possible pair.
III. LCM : 16 and HCF : 9. Product of the LCM and HCF = 16 * 9 = 144. However, the LCM 16 is NOT a multiple of the HCF 9. Hence, this one is also not a possible pair.