Product and G.C.D (interpreted as H.C.F): The product of two two-digit numbers is 2160 and their greatest common divisor is 12. Identify the numbers.

Difficulty: Medium

Correct Answer: 36 and 60

Explanation:


Introduction / Context:
For any two positive integers a and b, the relation a * b = GCD(a, b) * LCM(a, b) holds. When product and GCD are given, you can confirm candidate pairs by checking both the product and the GCD requirement.



Given Data / Assumptions:

  • a * b = 2160
  • GCD(a, b) = 12
  • a and b are two-digit numbers.


Concept / Approach:
Test options: both numbers must be multiples of 12 to have GCD 12 (not strictly necessary, but typical); more importantly, confirm GCD and product exactly. Dismissing pairs that fail the GCD check is fastest.



Step-by-Step Solution:

Option (36, 60): GCD(36, 60) = 12, product = 2160 ⇒ fits both conditions.Option (72, 30): GCD = 6 ⇒ fails GCD requirement.Option (96, 25): product 2400 ⇒ fails product; also GCD ≠ 12.Therefore, the valid pair is 36 and 60.


Verification / Alternative check:
Compute LCM using a * b / GCD = 2160 / 12 = 180. Indeed, LCM(36, 60) = 180, confirming consistency.



Why Other Options Are Wrong:
They fail either the stated GCD or the product condition. “None of these” is incorrect because a valid pair exists.



Common Pitfalls:
Assuming any factor pair of 2160 works without checking the GCD; or miscomputing the GCD due to incomplete factorization.



Final Answer:
36 and 60

More Questions from Problems on H.C.F and L.C.M

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