Tisch
Rounding method in addition and subtraction The quick and skillful calculation of addition and subtraction is mainly "rounding", that is, dividing the numbers in the formula into several groups, so that the operation results of each group are integer ten, integer hundred, integer thousand, and then adding (subtracting) the results of each group. Mainly involves several calculation methods:
(1) group rounding method (2) addition and complement rounding method (3) reference number method (4) bit value principle method.
Political methods in multiplication and division
In the multiplication and division method, we should first master the laws and properties of multiplication and division operation and the changing laws of product quotient in the operation, and then understand the characteristics of the purpose of solving problems, create conditions and choose reasonable and flexible calculation methods.
Calculation method: (1) Divide and merge method (2) Fast calculation of special numbers.
Rounding (the concept of quickly calculating special numbers)
The ten digits of the multiplicand and multiplier are the same, and the digits are complementary. This formula is called "head and tail complement"
The ten digits of multiplicand and multiplier are complementary, and the single digits are the same. This formula is called "the same head and tail".
For these two kinds of problems, there are very simple and quick calculation methods, namely, the "same complement" speed algorithm and the "same complement" speed algorithm.
The "same complement" speed algorithm is simply: the last two digits of the product are "tail× tail" and the front is "head× (head+1)"
The "complementary" speed algorithm simply means that the last two digits of the product are "tail× tail" and the front is "head× head+tail"
extreme
Calculate1(1)136+57+264+143.
(2) 168+253+532
(3)358+ 127+ 142+73
(4)( 1350+249+468)+(25 1+332+ 1650)
The specific analysis is as follows:
(1) The original formula = (136+246)+(57+143) = 400+200 = 600.
(2) The original formula = (168+532)+253 = 700+253 = 953.
(3) The original formula = (358+142)+(127+73) = 500+200 = 700.
(4) The original formula =1350+249+468+251+332+1650 = (1350+1650)+(249+250)
=3000+500+800=4300
Tisso
( 1)265-68- 132 (2)756-248-352
(3)268-56-82-44- 18
(4)83 1- 135-67- 145- 153
analyse
(1) Original formula = 265-(68+132) = 265-200 = 65.
(2) The original formula = 756-(248+352) = 756+600 =156.
(3) The original formula = 268-(56+44)-(82+18) = 268-100-100 = 68.
(4) The original formula = 831-(135+67+145+153) = 831-[(135+/kloc-)
Use the multiplication algorithm to show your talent, and you can record your quick calculation time.
( 1)99×4×25(2) 125× 1 19×8
(3) 125×72(4)25× 125× 16
Analysis because 25× 4 = 100, 125× 8 = 1000, 125× 4 = 500, using the commutative law and associative law of multiplication, try to combine 25 with 4, 125 with.
( 1)99×4×25=99×(4×25)=900
(2) 125× 1 19×8=( 125×8)× 1 19= 1 19000
(3) 125×72= 125×8×9= 1000×9=9000
(4)25× 125× 16=25× 125×2×8=(25×2)×( 125×8)=50× 1000=50000
Or 25×125×16 = 25×125× 4 = (25× 4 )× (125× 4) =100× 500 = 50000.