"Why is the number falling?"
Translation:Hvorfor er tallet faldende?
"tal" is a number, either a specific one, or just numbers. "antal" is a total of something. You can replace "antal" with "tal" when talking about a specific total of something, just like here, but not if you want to tell what you are counting; for example, "antallet af cykler" cannot be replaced by "tallet af cykler", while "antallet" can be replaced by "tallet". I hope this makes sense, but it is a little difficult to explain.