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9 + 1 = 10
3 + 4 = 17 => 17 = (3 + 4) + 10
15 + 3 = 35 => 35 = (15 + 3) + 17
=> 34 + 5 = (34 + 5) + 35 = 74
ĐÓ LÀ CÁCH GIẢI THEO TOÁN ĐỐ, CÓ QUY LUẬT
Theo theo cách giải đúng của toán học thì: 34 + 5 = 39
(1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20 ) -1-5-9-3=
= ( 1 + 20 ) x 20 : 2 - 1 - 5 - 9 - 3
= 210 - 1 - 5 - 9 - 3
= 192
hok tốt
bn rảnh ghê ha
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20-1-5-9-3=192
X = ( 1+10 ) * 10 / 2 = 11 * 10 / 2 = 110 / 2 = 55
X= (2+20) * 10 /2 = 110
X= (1+19)*10/2= 100
1+2+3+4+5+6+7+8+9+10= (10+1)X10 : 2 = 55
2+4+6+8+10+12+14+16+18+20 = (20+2)x10 : 2 = 110
1+3+5+7+9+11+13+15+17+19 = (19+1) x 10 : 2 = 100
Bài 1:Tính nhanh:
A,35x6-70x3+35=35
B,10+2+6+7+3+1+8+4+9+5=55
Bài 2:Tìm x:
x+779=4793
x=4793-779
x=4014
x-50374=87493
x=87493+50374
x=137867
xx3=6783
x=6783:3
x=2261
x:3=2967
x=2967x3
x=8901
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21=231
trả lời:
=231
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= 1+(2-3)+(4-5)+(6-7)+........+(18-19)+20
= 1+(-1)+(-1)+(-1)+........+(-1)+20
= 1+(-9)+20
= 12
(35 x 2 - 35:5 x 10) x (1 + 3 + 5 + ... + 19)
= [35 x 2 - 35 x (10 : 5) ] x (1 + 3 + 5 + ... + 19)
= (35 x 2 - 35 x 2) x (1 + 3 + 5 +... + 19)
= (70 - 70) x (1 + 3 + 5 + .... + 19)
= 0 x (1 + 3 + 5 + ... + 19)
= 0
(35 x 2 - 35: 5 x 10) x (1 + 3 + 5 + ... + 17 + 19)
= (70 - 7 x 10) x (1 + 3 + 5 + ... + 17 + 19)
= (70 - 70) x (1 + 3 + 5 + ... + 17 + 19)
= 0 x (1 + 3 + 5 + ... +17 + 19)
= 0