Question

A number has only 1 factor pair. One of its factors is twice the other factor. What is the number? Explain.

Answer 1

Answer:  2

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Explanation:

If a number only has one factor pair, then that number must be prime. This is because prime numbers only have factors of 1 and the number itself.

For instance, the value 7 is prime because the only factors of this are 1 and 7.

For something like the number 32, it is composite and not prime because it has the factors {1,2,4,8,16,32} and it leads to these three factor pairs: 1*32, 2*16, 4*8. This is one example showing why the answer isn't composite.

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Let's say that p is the unknown prime we want to find. The factors of this are 1 and p. We're told that "one of the factors is twice the other factor", so that must mean p = 2*1 = 2. We can see that 2 is twice that of 1.