Folmula Help

Hello Olivia, 

I think it's easier if you just create one or() with all the conditions there. 
I believe I got all your requirements on this formula, please make sure the strings are correct: 

or(
greaterThan($riskpercentage_c,25),
isInList($sales_stage,createList("Closed Lost","Pending_Cancellation")),
and(equal($lost1_c,"Product Performance"),equal($lost3_product_c,""))
)

I get this error greaterThan: The parameter at index 0 must be of type number.

Field riskpercentage is a dropdown list.

I have fixed that bit but it is still not working for the last condition. It needs to be only required if these two are both true $lost1_c,"Product Performance"),equal($lost3_product_c,""

I get this error greaterThan: The parameter at index 0 must be of type number.

Field riskpercentage is a dropdown list.

I have fixed that bit but it is still not working for the last condition. It needs to be only required if these two are both true $lost1_c,"Product Performance"),equal($lost3_product_c,""