i have custom field called Revenue on opportunity object the condition is, if lead source is web and the amount is greater than 1000 then the revenue is 2% of the amount.
if lead source is web and the amount is lesser than 1000 then the revenue is 1% of the amount.
if lead source is apart from the above  then the revenue is 25% of the amount.
 

On Opportunity whem an trying to change the stage from  prospecting to qualification. it should throw an error based on the condition..if type is new customer ,then the amount show be grater than 100.how can we achieve through validation rule

i have custom field called Revenue on opportunity object the condition is, if lead source is web and the amount is greater than 1000 then the revenue is 2% of the amount.
if lead source is web and the amount is lesser than 1000 then the revenue is 1% of the amount.
if lead source is apart from the above  then the revenue is 25% of the amount.
 

On Opportunity whem an trying to change the stage from  prospecting to qualification. it should throw an error based on the condition..if type is new customer ,then the amount show be grater than 100.how can we achieve through validation rule