If I saved up $10 every 2 weeks, in a year I would have saved up $260. But, if I had saved up $20 per month, I would only have saved $240. Why do they have different totals?

They have different totals because the 10 dollars your putting in every 2 weeks. Now with the 20 dollars you doing it every month so they have different totals because ones getting put in every month and the other is getting put in every 2 weeks.