Ideally, we would want to populate the Weighted Value field with the result of the formula (Estimated Value X (Probability/100)). Unfortunately, this is not possible in a single step using a workflow.
You will need 3 Update Steps as shown below:
Here are the details of each Update Step:
Step 1: Create a Workflow on the Opportunity entity.
Step 2: This Workflow should “Start when”:
Record is created
Estimated Revenue or Probability is changed
Step 3: Add an Update Opportunity step and populate the “Est Revenue” value into the “Weighted Value” field.
Step 4: Add an Update Opportunity step and multiply the “Weighted Value” field by the Probability.
Step 3: Add an Update Opportunity step and divide the “Weighted Value” field by 100.