The ingenious calculation method of mathematics in grade three is very useful for children to do their homework.
"Round up" first.
1. Calculation:
The ingenious calculation method of mathematics in grade three is very useful for children to do their homework.
( 1)24+44+56 (2)53+36+47
Solution: (1) 24+44+56 = 24+(44+56) = 24+100 =124.
Because 44+56= 100 is an integer, let's calculate their sum first.
(2)53+36+47=53+47+36 =(53+47)+36= 100+36= 136
Because 53+47= 100 is an integer, move +47 together with the symbol and before +36; Then calculate the sum of 53+47.
2. Calculation:
( 1)96+ 15 (2)52+69
Solution: (1) 96+15 = 96+(4+11)
=(96+4)+ 1 1= 100+ 1 1= 1 1 1
Divide 15 into 15=4+ 1 1, because 96+4= 100 can be rounded first.
(2)52+69=(2 1+3 1)+69 =2 1+(3 1+69)=2 1+ 100= 12 1
Because 69+3 1= 100, 52 is divided by the sum of 2 1 and 3 1, and then 3 1+69= 100 is rounded up first.
3. Calculation:
( 1)63+ 18+ 19 (2)28+28+28
Solution: (1) 63+18+19 = 60+2+18+19 = 60+(2+/kloc-0
Divide 63 by 63=60+2+ 1 because 2+ 18 and 1+ 19 can be rounded first.
(2)28+28+28 =(28+2)+(28+2)+(28+2)-6 =30+30+30-6=90-6=84
Because 28+2=30 can be rounded, but in the end, we still have to subtract the extra three 2' s.
The ingenious calculation method of mathematics in grade three is very useful for children to do their homework.
Change the operation order
In a mixed formula with only "+"and "-",the operation order can be changed.
Calculation: (1) 45-18+19 (2) 45+18-19.
Solution: (1) 45-18+19 = 45+19-18 = 45+(19-18).
Move the symbol+19 before-18. Then calculate 19- 18= 1.
(2)45+ 18- 19=45+( 18- 19)=45- 1=44
Adding 18 and subtracting 19 equals subtracting 1.
The ingenious calculation method of mathematics in grade three is very useful for children to do their homework.
The ingenious calculation method of mathematics in grade three is very useful for children to do their homework.
Calculate the sum of arithmetic continuous numbers
A string of numbers with equal difference between two adjacent numbers is called arithmetic hyphen, also called arithmetic progression, such as:
1,2,3,4,5,6,7,8,9
1,3,5,7,9
2,4,6,8, 10
3,6,9, 12, 15
4, 8, 12, 16, 20 and so on are arithmetic hyphens.
1. When the number of arithmetic hyphens is odd, their sum is equal to the middle number multiplied by the number, abbreviated as:
(1) calculation: 1+2+3+4+5+6+7+8+9 =5 (median is 5) × 9 (* * 9 number) =45.
(2) Calculation: 1+3+5+7+9 =5 (median is 5)×5 (*** has five numbers) =25.
(3) Calculation: 2+4+6+8+ 10 =6 (median is 6 )×5 (*** has five numbers) =30.
(4) Calculation: 3+6+9+ 12+ 15 =9 (median is 9)×5(*** has five numbers) =45.
(5) Calculation: 4+8+12+16+20 =12 (median is 12) × 5 (* * has five numbers) =60.
2. When the number of arithmetic hyphens is even, their sum is equal to the sum of the first number and the last number multiplied by half of the number, abbreviated as:
(1) calculation:1+2+3+4+5+6+7+8+9+10 = (1+kloc-0/0) × 5 =1.
*** 10 number, the half number is 5, the first number is 1, and the last number is 10.
(2) Calculation: 3+5+7+9+11+13+17 = (3+17) × 4 = 20×
* * * No.8, the half number is 4, the first number is 3, and the last number is 17.
(3) Calculation: 2+4+6+8+10+12+14+16+18+20 = (2+20) × 5 =/kl.
*** 10 number, the half number is 5, the first number is 2, and the last number is 20.
The ingenious calculation method of mathematics in grade three is very useful for children to do their homework.
Benchmark number method
(1) calculation: 23+20+19+22+18+21.
Solution: After careful observation, the size of each addend is close to 20. You can first add up each addend according to 20, and then add up the less calculated ones and subtract the more calculated ones.
23+20+ 19+22+ 18+2 1
=20×6+3+0- 1+2-2+ 1
= 120+3= 123
All six addends add 20, and the sum =20×6= 120.23. If calculated by 20, "3" is missing, so "3" is added; 19 Add "1" to 20, so subtract "1" and so on.
(2) Calculation:102+100+99+101+98.
Method 1: After careful observation, we can see that each addend is close to 100, so we choose 100 as the benchmark number and skillfully use the benchmark number method to calculate. 102+ 100+99+ 10 1+98 =
Method 2: After careful observation, the five numbers can be rearranged as follows: (In fact, some addends move with signs)
102+ 100+99+ 10 1+98 =98+99+ 100+ 10 1+ 102 = 100×5=500
It can be found that this is a summation problem of arithmetic connected numbers, the middle number is 100, and the number is 5.