678+456=600+70+8+400+50+6=600+400+70+50+8+6= 1 134
It's really better to break it down into integers. In fact, the column is not just a point that children forget to carry.
Oral addition is relatively easy. Let's try double-digit multiplication again. I think it is really difficult to get rid of vertical multiplication. 74× 12=? Let's take a look at the slow-motion playback of mental arithmetic in the book:
74× 12=74×( 10+2)=74× 10+74×2=888
The operation process is shown in this way, and children can understand it. Multiplying by whole ten is really simple.
I've tried the decimal problem. Children have never learned it, so I experienced it alone, because the decimal problem is easy to make mistakes, especially when the number of digits after the decimal point is different, and the column is vertical.
3.5- 1.5 1=? First, subtract 1.5 from the previous two terms to get 2-0.0 1= 1.99. In the book, the numbers in the formula are simplified to an integer and a decimal by intensity subtraction. After understanding this problem, it is not difficult to understand the next one.
Decimal conversion: 49÷87.5=? 49÷87.5=0.49÷0.875=0.49÷7/8=0.49×8/7=0.56
Second, the mathematical formula, can learn is limited, we should expand the part that we can't learn.
The book 10 Double Speed Mental Arithmetic is a collection of different mental arithmetic methods. Mental arithmetic is actually looking for the law between numbers. Faced with different formulas, I can find the simplest method among many problem-solving schemes. This is my initial cognition. In fact, I really need to remember the method and then apply it. However, there are many methods in the book 10 times speed mental arithmetic, which actually feels more than application. More often, I can remind myself how to calculate simply through digital association and operation symbols. Of course, familiarity with methods is the foundation, so that ideas can be opened. This is the part of knowledge that can't be learned in this book column. It is a method that is independently explored and summarized after mastering various calculation methods. It really takes some skill to reach this level.