![](https://rs.olm.vn/images/avt/0.png?1311)
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
462 – 40 + 7 = 422 + 7
= 429
387 – 7 – 80 = 380 - 80
= 300.
![](https://rs.olm.vn/images/avt/0.png?1311)
Tính :
A = 1 + 2 + 3 + 4 + 5 + 5 + 6 + 7 + 8 + 9 + 10
A = ( 1 + 9 ) + ( 2 + 8 ) + ( 3 + 7 ) + ( 4 + 6 ) + ( 5 + 5 ) + 10
A = 10 + 10 + 10 + 10 + 10 + 10
A = 60
B = 10 + 20 + 30 + 40 + 50 + 50 + 60 + 70 + 80 + 90 + 100
B = ( 10 + 90 ) + ( 20 + 80 ) + ( 30 + 70 ) + ( 40 + 60 ) + ( 50 + 50 ) + 100
B = 100 + 100 + 100 + 100 + 100 + 100
B = 600
![](https://rs.olm.vn/images/avt/0.png?1311)
20 x 20 = 400
40 x 40 = 1 600
60 x 60 = 3 600
80 x 80 = 6 400
100 x 100 = 10 000
ủng hộ mk nhé
![](https://rs.olm.vn/images/avt/0.png?1311)
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9
= (1 + 9) + (2 + 8) + (3 + 7) + (4 + 6) + 5
= 10 + 10 + 10+ 10 + 5
= 45
10 + 20 + 30 + 40 + 50 + 60 + 70 + 80 + 90
= (10 + 90) + (20 + 80) + (30 + 70) + (40 + 60) + 50
= 100 + 100 + 100 + 100 + 50
= 450
1237 + 2249 + 1763 + 2251
= (1237 + 1763) + (2249 + 2251)
= 3000 + 4500
= 7500
1+2+3+4+5+6+7+8+9= 45
10+20+30+40+50+60+70+80+90 = 450
1237+2249+1763+2251 = 7500
![](https://rs.olm.vn/images/avt/0.png?1311)
20 × 20=400
40 × 40=1600
60 × 60 =3600
80 × 80=6400
100 × 100=10000
= 268
= 217
= 429
= 300
205 + 60 + 3 = 268
268 - 68 + 17 = 217
462 - 40 + 7 = 429
387 - 7 - 80 = 300