Question

John is finding the factors of a large number. Using a calculator, he has just worked out that 20 is a factor of this number. Suddenly, he realizes that 4 must be a factor of the large number as well. Why is John correct?

Answer 1

John is correct because if a number is divisible by 20, it is also divisible by all the factors of 20, including 4.

Step-by-step explanation:

John is correct that 4 must be a factor of the large number because if a number is divisible by 20, it is also divisible by all the factors of 20. Since 20 can be expressed as 2 x 2 x 5, we know that any number divisible by 20 must also be divisible by 2 and 5. Therefore, since John has already determined that 20 is a factor, it follows that 4 (2 x 2) must also be a factor of the large number.