To find the percentage change from 90 to 50, we need to first calculate the difference between the two numbers.

Step 1: Difference = Final Value - Initial Value

Difference = 50 - 90

Difference = -40

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 = |-40|

Absolute Difference = 40

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

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

Percentage Change = (40 / 90) x 100

Percentage Change = 44.44%

Therefore, the percentage change from 90 to 50 is -44.44%. This means that there was a decrease of 44.44% from 90 to 50.