To find the percentage change from 20 to 10, we need to first calculate the difference between the two numbers.

Step 1: Difference = Final Value - Initial Value

Difference = 10 - 20

Difference = -10

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 = |-10|

Absolute Difference = 10

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

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

Percentage Change = (10 / 20) x 100

Percentage Change = 50%

Therefore, the percentage change from 20 to 10 is -50%. This means that there was a decrease of 50% from 20 to 10.