372.70973 MA(166p)
dividend ÷ divisor = quotient
Multiplier(factor, number of group ) * multiplicand(factor: number in a group) = Product,
google search : devlin on multiplication(Keith Devlin): multiplication is not repeated addition., no mention in this book.
Worth reading for parents try to help their children and teachers try to teach elementary arithmetic(addition, subtraction, multiplication, division). A great insight of elementary math teaching, procedural perspective teaching vs. Conceptual perspective teaching. Some arguments are very strong and persuasive, but I doubt the children can fully standard them.
My reading note:
1)Chapter1 subtraction with regrouping
A:decomposing a higher value unit p7
B:the rate of composing a higher value unit:10, which is 10 lower place value = 1 higher place value and the place value system addressing in chapter 2 are theories underneath addition, subtraction standard carrying or borrowing procedural algorithm, you always deal with number under 20. e.g 1536 - 722, after borrow one from 5, 5 become 4, 3 become 13, which actually 13 hundreds - 7 hundrends. see more on book p 42 - p43(multiplication), which make algorithm always work.
C.my thought of place value: the core of multiplication is another thinking place value idea.In multiplication decimal system unit value change from one unit, to tens unit, .... to justification move algorithm, you can also think as unit is multiplicand
D: Borrowing traditional term will illustrate standard subtraction procedure. lower place is "BORROW" from higher place.
I don't totally agree with author that decomposing should substitute borrowing term. Decomposing emphasis the "no value change" idea, borrowing illustrate subtraction procedure, they are 2 faces of the same thing.
2) Chapter 2: multidigit number multiplication.
p32-35 Ample evidence of teachers own incompetence regarding math subject knowledge. It remind me Finnish teachers high quality with master degree in subject discipline teaching. A huge concern
Observation:
Why my child start doing math from higher value place (left) instead of lower value place?
It puzzles me until I saw explanation on p20. We do it all the time even we are not fully aware of it. Example, how change I can get after paying $2 for something cost 1 dollars 63 cents. We first subtract 1 dollar, then rest 63 cents. That my daughter does whenever doing addition and subtraction, she has a strong concept with carrying and borrowing concept, keeping change value when she found carrying or borrowing happen, she figure out her idea's math operation rule when playing monopoly game. There is a great advantage doing this way, we can quick figure out how big the number is, get a rough idea. But doing in school standard way, when one column value is done it will fixed, it is logarithm, applied to any occasion, a great for computer: fixed prove procedure. but not always a best choice for some problem. That is why computers are best at boring unchanged satiation, such like calculating our bank balance, worse at artificial intelligence, such as pattern recognition, I like computer can be our friend help things our human not good at, instead of enemy.
Summary:
1. High concern about cramming arithmetic teaching (calculation teaching) in elementary school even it could be done correctly. Neuroscience study shows our brain (cortex) dealing with abstract number operations not fully mature until adolescence. Teachers have to use manipulative to address simple math operation, such as 12 - 3. What is so different from take 3 apples from 12 apples to 12 - 3?
Dealing with apples so easy for children instead of purely math? The great invention of mathematics is a huge achievement ever human being made. The map from real world problems to abstract math world is a great leap that distinguish us from other animals. These abstract thinking are last physically developed in our brain. Too early to teach such knowledge not fitted to children brain level can bring a huge damage: lack creativity, less confidence.
2. Stop teaching arithmetic instead of focus on math concept teaching, like ratio, percentage, geometry, graph, even chaos, fractal or basically math history are well within children brain level.
“If you can't explain it to a six year old, you don't understand it yourself.”
― Albert Einstein
Commutative law of addition: m + n = n + m
Commutative law of multiplication: m · n = n · m
Associative law of addition: ( m + n ) + k = m + ( n + k ) = m + n + k
Associative law of multiplication: ( m · n ) · k = m · ( n · k ) = m · n · k
Distributive law of multiplication over addition: ( m + n ) · k = m · k + n · k
Math teaching
1. Why Roman numerical system(I, II, IX,) inferior to Arabic numerical system (1,2 3,4): not straight, involving addition when figure number out, e.g. IX (4) = X(5) - I(1)
2. (a1/b1)/(a2/b2) = (a1/a2) /(b1/b2)
3. rate of higher place value of 10 underline carry, borrowing procedure
3. Chinese number system advantage, forty means five tens in chinese, 五十 五个十