Transcript ppt file

Caculation Skills
MULTIPLICATION
DIVISION
power
If the top digits of dividend and the divisor is the
same , in addition the first two digits of the dividend
is not enough. At this time, the first digit of quotient
was 8 or 9.
EX.5742÷58=99，4176÷48=87
57<58
574compare 58*9=522
against 58*8=464
The first digit of quotient
is 9
When the first two digits of the number of interim dividend
consisting of less than the divisor and the first three digits of the
number of provisional composition of the divisor and greater than
or equal to 10 times of the divisor,the quotient can be a digit of
"9."
Generally, if the dividend is m, the divisor is n, only when 9n ≤ m
<10n, n divide m is 9. This is the gist of the method.
EX. 4508÷49=92，6480÷72=90
When the divisor is 11, 12 ............ 18 and 19, and in addition to the
first two digit of the dividend is not enough to be divided by
dividor, you can use method to know the first digit of the quotient
according to the difference between the divisor and the first two
digit of the dividend.
EX. 1476÷18=82（the difference between 18 and 14 is
the first digit of the
The
difference
4，so the first digit of the quotient
is 8）；
quotient
9 17 and 12 is 5，
1 、2 difference between
1278÷17=75（the
8
the first digit of35 、4
the
quotient
is
7）。
7
、6
7 、8
9
6
5
23×27=？
2×（2+1）=6
3×7=21
Result:621
Explanation:
When a＋b＝10，
（A×10＋a）（A×10＋b）
= A×A×100+A×（a+b）×10+ab
=A×(A＋１)×100＋ab
18×98=?
17=1×9+8
64=8×8
Result:1764
Explanation:
When A+B=10
（A×10+a）（B×10+a）
=（AB+a）×100+a^2
32×28=?
3 is the bigger one of the tens digits.
8=3×3-1.
2 is the bigger units digit of the two number.
96=100-2×2.
Result:896
Explanation:
（A×10+a）×[(A-1)×10＋(10-a)]
=(A^2-1)×100+(100-a^2)
66×37=?
24=6×(3+1)
42=6×7
Result:2442
Explanation:
when a+b=10
（A×10＋A）（a×10＋b）
=A(a＋1)×100＋Ab
learn from a2=(a+b)(a-b)+b2
EX
152=(15+5)x(15-5)+52
532=(53+3)x(53-3)+32
EXPAND
8632=900x?+372
Because the difference between 900 and 863 is the same as that
between 900 and ?, so 900+? must be twice as much as 863.
?-800=63x2-100=26
8632=900x826+372
372=40x34+3^2
How about cube?
we know that
a3=aa2=a(a2-b2)+ab2
=a(a+b)(a-b)+ab2 Either a+b or a-b is times as much as 10, it
would be the best if they both are.
EX 133=10x13x16+13x32
way easier?
Let’s play a game
1
X
2
Y
3
X+Y
4
X+2Y
5
2X+3Y
6
3X+5Y
7
5X+8Y
8
8X+13Y
9
13X+21Y
10
21X+34Y
TOTAL
55X+88Y
Xu ZeYu 13122674
Zhu WeiTao 13122041
Hu Chao 13121197