How does moving the place of a digit change its value

Moving places of a digit changes its value.

We can see the following example.

Say we have a number 1234.

We have 1 at thousand place with a value of 1000.

We have 2 at hundreds place with a value of 200.

We have 3 at tens place, with a value of 30.

We have 4 at ones place with a value of 4.

Say we interchange the numbers and make it 4321.

Now we have 4000 , then 300, then 20 then 1.

We can see that the 4 at ones place is just 4 but at thousand place, its value is 4000.

Hence, it is clear that moving the place of a digit change its value.

the answer is 31.27mph