Multiple choice

The HCF of two numbers is 25 and the HCF of other two numbers is 15. What is the HCF of all the four numbers?

  1. 50

  2. 45

  3. 15

  4. 5
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D Correct answer
Explanation

The HCF of two numbers is a factor of those numbers. If HCF(a,b)=25 and HCF(c,d)=15, the HCF of all four must be a common factor of 25 and 15, which is 5.

AI explanation

The HCF of a set of numbers must be a common factor of all of them, so the HCF of all four numbers must be a common factor of both 25 and 15. The factors of 25 are 1 and 5, while the factors of 15 are 1, 3, 5, and 15. The greatest common factor shared by both groups is 5. The HCF of all four numbers is 5.

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