More than 300 million of these have been sold since being invented. What are they? Getty Images October 10, 2018 Q: More than 300 million of these have been sold since being invented. What are they? A: Slinky’s SHARE RELATED CONTENT In Arizona, you have to have a permit to do THIS with your garbage, What is it? This is true for 7% of weddings. What is it? The #1 thing Americans say they don’t get enough of is .. SLEEP. What is #2 on the list? John: It’s A Miracle We Survived… This was true for US Presidents until 1974. What is it? About 30% of doctors admit to doing THIS more than once. What is THIS?