500 is half of one thousand so 500 times 523 is 1/2 of 523000. Can you do 523000/2 in you head?

489 is 11 less than 500 so after you have 500 times 523, you still need to subtract 11 times 523. What is 10 times 523? Can you subtract that from the 523000/2 you already have? The subtract it once more.