Using each of the numbers 1 to 9 once and once only, find two whole numbers, one of which is double the other?

Solution:

Given domain={1,2,3,4,5,6,7,8,9}

Consider the first number as 1, the double of 1 will be 2.

So, one whole number could be “1”.

Consider the second number as 2, the double of 2 will be 4.

So, the other whole number could be “2”.

Similarly, there can be 3 doubles as 6 and 4 doubles as 8.

If we take 5, its double is 10 which is not in the given range.

Therefore, the required whole numbers that form our range is {1,2,3,4}.

Using each of the numbers 1 to 9 once and once only, find two whole numbers, one of which is double the other?

Summary:

Using each of the numbers 1 to 9 once and once only, the two whole numbers, one of which is double the other can be either 1 or 2 or 3 or 4.