Recognizing that 8 is near to 10 provides a simple strategy for learning +8 number facts.
Adding 8 or 9, which otherwise would be quite challenging, is quite easy if you think of adding 10 and then adjusting the result.
Actually, there are at least two similar methods to use for a number fact such as “5 + 8”:
Whichever strategy is used, the intention is for students to understand the strategy and apply it mentally, not to write down the intermediate steps as I have done above.
