Adding 9 and 99: The Sticker Shop

At the Sticker Shop, Zoe and Mia sell big sheets of 10 heart stickers and little sheets of 9 star stickers. Adding 9 is easy when you remember it is just 1 less than 10!

Remember: To add 9, add 10 and take away 1: 46 + 9 = 56 − 1 = 55. To add 99, add 100 and take away 1: 245 + 99 = 345 − 1 = 344. To take away 9, take away 10 and add 1 back: 63 − 9 = 53 + 1 = 54.

Magic trick: 9 is a 10 that lost 1, and 99 is a 100 that lost 1. Jump the round number, then step back 1.