To find the percentage change from 200 to 100, we need to first calculate the difference between the two numbers.

Step 1: Difference = Final Value - Initial Value

Difference = 100 - 200

Difference = -100

Step 2: Next, we need to find the absolute value of the difference. This is because percentage change is always calculated as a positive value.

Absolute Difference = |Difference|

Absolute Difference = |-100|

Absolute Difference = 100

Step 3: Now, we can calculate the percentage change using the formula:

Percentage Change = (Absolute Difference / Initial Value) x 100

Percentage Change = (100 / 200) x 100

Percentage Change = 50%

Therefore, the percentage change from 200 to 100 is -50%. This means that there was a decrease of 50% from 200 to 100.