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147abc = 3 x 7 x 7 x a x b x c

Basically, you use prime factorization x variables.

Non-examples are infinite. One relevant one is a number that cannot be divided into a number.

Since 18 is a factor of 90 and it is the largest factor of itself, the greatest common factor of 18 and 90 is 18.

Since 18 is a factor of 90, it is automatically the GCF.

1 x 330, 2 x 165, 3 x 110, 5 x 66, 6 x 55, 10 x 33, 11 x 30, 15 x 22

It is not possible to give a sensible answer to this question. The least common multiple (LCM) refers to a multiple that is COMMON to two or more numbers. You have only one number in the question!

20

To find a missing factor you need an equation. Is this supposed to be 4f = 11?

Then the answer is f = 11/4 or 2 3/4 or 2.75

To find the HCF of two numbers you first need to express them as the product of their prime factors. In this case you'd get:

45 = 3x3x5

60 = 2x2x3x5

The next step is to identify any common prime factors. In this case both numbers have a 3 and a 5 as a prime factor. Multiplying these together gives:

3x5 = 15

And so 15 is the HCF of 45 and 60.

There are infinitely many such pairs of numbers. As long as the only primes they have in common are 2×3²×5 (the prime factorization of 90) their gcf will be 90:

Some examples:

90, 180

90, 270

90, 360

180, 270

180, 450

450, 630

630, 990