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Caculation Skills. MULTIPLICATION DIVISION power.

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Presentation on theme: "Caculation Skills. MULTIPLICATION DIVISION power."— Presentation transcript:

1 Caculation Skills

2 MULTIPLICATION DIVISION power

3 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=522 58*8= compare against The first digit of quotient is 9

4 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

5 When the divisor is 11, 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 difference the first digit of the quotient 1 、 、 、 、 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 )。

6 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

7 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

8 32×28=? 3 is the bigger one of the tens digits. 8=3× 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)

9 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

10 learn from a 2 =(a+b)(a-b)+b 2 EX 15 2 =(15+5)x(15-5) =(53+3)x(53-3)+3 2 EXPAND =900x?+37 2 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= =900x =40x34+3^ 2

11 How about cube? we know that a 3 =aa 2 =a(a 2 -b 2 )+ab 2 =a(a+b)(a-b)+ab 2 Either a+b or a-b is times as much as 10, it would be the best if they both are. EX 13 3 =10x13x16+13x3 2 way easier?

12 Let’s play a game

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14 Xu ZeYu Zhu WeiTao Hu Chao


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