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a: =24/15-18/15=6/15=2/5
b: =78/42-24/42=54/42=9/7
c: =30/36-12/36=18/36=1/2
d: =7/8-1/8-3/34=6/8-3/34=3/4-3/34=45/68
![](https://rs.olm.vn/images/avt/0.png?1311)
Tính nhanh:
\(10+20+30+40+50+60+70+80+90+100\)
\(=\left(10+90\right)+\left(20+80\right)+\left(30+70\right)+\left(60+40\right)+50+100\)
\(=100+100+100+100+150\)
\(=550\)
Tính:
40 + 1 230 = 1 270
1 230 + 40 = 1 270
67 478 + 9 076 = 76 554
9 076 + 67 478 = 76 554
Tính nhanh:
10 + 20 + 30 + 40 + 50 + 60 + 70 + 80 + 90 + 100
= (10 + 90) + (20 + 80) + (30 + 70) + (40 + 60) + (100 + 50)
= 100 + 100 + 100 + 100 + 150
= 100 \(\times\) 4 + 150
= 400 + 150
= 550
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{10}+\frac{2}{20}+\frac{3}{30}+\frac{4}{40}+\frac{5}{50}+\frac{6}{60}+\frac{7}{70}+\frac{8}{80}+\frac{9}{90}\)
\(=\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}\)
\(=\frac{9}{10}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
10 + 20 + 30 + 40 + ... + 50 + 60 + 70 + 80 + 90 + 100
=100 + ( 90 + 10 ) + ( 80 + 20 ) + ( 30 + 70 ) + ( 40 + 60 ) + 50
=100 + 100 + 100 +100 + 100
= 100 x 5 + 50
= 500 + 50
= 550
10 + 20 + 30 + 40 + .... + 50 + 60 + 70 + 80 + 90 + 100
= ( 10 + 90 ) + ( 20 + 80 ) + ( 30 + 70 ) + ( 40 + 60 ) + 50 + 100
= 100 + 100 + 100 + 100 + 50 + 100
= 100 x 4 + 50
= 400 + 50
= 450
![](https://rs.olm.vn/images/avt/0.png?1311)
(10+90)+(20+80)+(30+70)+(40+60)+50
=100+100+100+100+50
=100x4+50
=400+50
=450
10 + 20 +30 + 40 + 50+ 60 + 70 + 80 + 90
= ( 10 + 90 ) + ( 20 + 80 ) + ( 30 + 70 ) + ( 40 + 60 ) + 50
= 100 + 100 + 100 + 100 + 50
= 450
k mik nha làm ơn đó
![](https://rs.olm.vn/images/avt/0.png?1311)
A = 10 + 20 + 30 + 40 + 50 + 60 + 70 + 80 + 90
A = ( 10 + 90) + (20 + 80 ) + ( 30 + 70 ) + (40 + 60 ) + 50
A = 100 + 100 + 100 +100 + 50
A = 400 + 50
A = 450
chúc bn hk tốt nhé !
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
1/10 + 4/20 + 9/30 + 16/40 + 25/50 + 36/60 + 49/70 + 64/80 + 81/90
= 1/10 + 2/10 + 3/10 + 4/10 + 5/10 + 6/10 + 7/10 + 8/10 + 9/10
=(1+2+3+....+9) /10
=(1+9)x9:2 /10
=45/10=4,5
chắc chắn đúng đó
41
-1
tick minhf nha
42:2+40:2=21+20=41
90:10-80:10=9-8=1