Question

Bài 1: Tính bằng cách thuận tiện nhất

a/ 457 + 218 + 143 b/ 346 + 412 + 188 c/ 8 phần 9 + 14 phần 27 + 1 phần 9

d/ 1 phần 2 + 3 phần 4 + 1 phần 2 e/ 3,17 x 8,9 + 8,9 x 6,83 f/ 1 + 3 + 5 + ... + 19.

Answer 1

457+218+143=(457+143)+218=600+218=818

b/ 346 + 412 + 188=346+(412+188)=346+600=946

\(c,\dfrac{8}{9}+\dfrac{14}{27}+\dfrac{1}{9}=\left(\dfrac{8}{9}+\dfrac{1}{9}\right)+\dfrac{14}{27}=1+\dfrac{14}{27}=\dfrac{41}{27}\)

d,\(\dfrac{1}{2}+\dfrac{3}{4}+\dfrac{1}{2}=\left(\dfrac{1}{2}+\dfrac{1}{2}\right)+\dfrac{3}{4}=1+\dfrac{3}{4}=\dfrac{7}{4}\)e,3,17.8,9+8,9.6,83=8,9(3,17+6,83=8,9.10=89

Answer 2

a)

457 + 218 + 143

= (457 + 143) + 218

= 600 + 218

= 818

b)

346 + 412 + 188

=346 + (412 + 188)

=346 + 600

= 946

c)

\(\dfrac{8}{9}+\dfrac{14}{27}+\dfrac{1}{9}=\left(\dfrac{8}{9}+\dfrac{1}{9}\right)+\dfrac{14}{27}=1+\dfrac{14}{27}=\dfrac{27}{27}+\dfrac{14}{27}=\dfrac{41}{27}.\)

d)

\(\dfrac{1}{2}+\dfrac{3}{4}+\dfrac{1}{2}=\left(\dfrac{1}{2}+\dfrac{1}{2}\right)+\dfrac{3}{4}=1+\dfrac{3}{4}=\dfrac{4}{4}+\dfrac{3}{4}=\dfrac{7}{4}.\)

e)\(\)

3,17 x 8,9 + 8,9 x 6,83 = 8,9 x ( 3,17 + 6,83 )

= 8,9 x 10

= 89

f)

1+3+5+...+19

= (19+1)+(17+3)+(15+5)+(13+7)+(11+9)

= 20+20+20+20+20

= 20 x 5

= 100