Question

bài 1: tính nhanh

a, (1+2+3+4+5+6+7+8+9)

b, 12+13+7+8

c, 50+60+50+40

Answer 1

a, 1+2+3+4+5+6+7+8+9=

(1+9)+(2+8)+(3+7)+(4+6)+5

=10+10+10+10+5

=45

b,(12+8)+(13+7)

=20+20

=40

c,(50+50)+(60+40)

=100+100

=200

Answer 2

(1+2+3+4+5+6+7+8+9)=45

12+13+7+8=40

50+60+50+40=200

Answer 3

45 đó

40 nha

200 đó

Answer 4

a)45

b)40 

c)200

Answer 5

a) 45

b)40

c) 200

Answer 6

a, 1+2+3+4+5+6+7+8+9

= (1+9)+(2+8)+(3+7)+(4+6)+5

= 10+10+10+10+5

= 10x4+5

= 40+5

=45

b, 12+13+7+8

= (12+8)+(13+7)

= 20+20

= 40

c, 50+60+50+40

= (50+50)+(60+40)

= 100+100

= 200