Caculation Skills

MULTIPLICATION MULTIPLICATION

DIVISION DIVISION

power 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 58*9=52258*8=464

574compareagainst

The first digit of quotientis 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.

The differencethe first digit of the

quotient1 、 2 93 、 4 85 、 6 77 、 8 6

9 5

EX. 1476÷18=82 （ the difference between 18 and 14 is 4 ， so the first digit of the quotient is 8）；1278÷17=75 （ the difference between 17 and 12 is 5 ， the first digit of the quotient is 7）。

23×27=？

2× （ 2+1 ） =6 3×7=21Result:621Explanation: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+864=8×8Result:1764Explanation: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:896Explanation:（ A×10+a） ×[(A-1)×10 ＋ (10-a)]=(A^2-1)×100+(100-a^2)

66×37=?

24=6×(3+1)42=6×7Result:2442Explanation: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

Xu ZeYu 13122674Zhu WeiTao 13122041Hu Chao 13121197