The “9-trick”: To add 9 to any number, first add 10, and then subtract 1. Can you think of an easy way to add 76 + 99? Change it to 75 + 100. How about 385 + 999? How would you add 39 + 28 in your head? Let 39 become 40… which reduces 28 to 27. The…
The “9-trick”: To add 9 to any number, first add 10, and then subtract 1. Can you think of an easy way to add 76 + 99? Change it to 75 + 100. How about 385 + 999? How would you add 39 + 28 in your head? Let 39 become 40… which reduces 28 to 27. The…