Updating a record with math and division

Ok.... So to update a record lets say... I have a current value of 150 and the new value will be 250 now how would I total them to equal 400? I was thinking $sql = "UPDATE $table value1 = value1 + ? is that correct? how do you update it with simple math? What about division... take the current value in the database + the new value divided by another number, lets say another field