①6+6=+2= 12

②7 16 =+3 = 13

③8 16 =+4 = 14

④9+6=+5= 15

⑤9 17 = 16 = 16

⑥5 ten 8=8 ten 5=+3= 13

Wait, take the smaller addend apart.

Add a larger addend to 10, and then add a disassembled addend, and you can directly see the result, which belongs to the basic knowledge of mental arithmetic.

Second, the method of breaking ten → is to separate the 10 of the minuend that is greater than 10 and less than 20 when the subtraction operation is performed within 20, which makes the operation reasonable and simple. For example:

① 17-8= 10+7-8= 10-8+7=9

② 15 a7 = 10 15 a7 = 10 a7+5 = 8。

③ 16 A8 = 10 16 A8 = 10 A8+6 = 8。

④ 13 One 5= 10 Ten 3-5= 10-5+3=8.

⑤ 13-8= 10+3-8= 10-8+3=2+3=5

Wait, these basics are very important.