Question

Tính bằng cách thuận tiện nhất:

a) \(\left(689+875\right)+125\);                                    \(581+\left(878+419\right)\).

b) \(\left(\dfrac{2}{7}+\dfrac{4}{9}\right)+\dfrac{5}{7}\);                                        \(\dfrac{17}{11}+\left(\dfrac{7}{15}+\dfrac{5}{11}\right)\).

c) \(5,87+28,69+4,13\);                                \(83,75+46,98+6,25\).

Answer 1

Answer 2

a) (689 + 875) + 125

= 689 + (875 + 125)

= 689 + 1000 = 1689.

581 + (878 + 419)

= (581 + 419) = 878

= 1000 + 878 = 1878.

b)

c) 5,87 + 28,69 + 4,13

= (5,87 + 4,13) + 28,69

= 10 + 28,69

= 38,69.

83,75 + 46,98 + 6,25

= (83,75 + 6,25) + 46,98

= 90 + 46,98

= 136,98.

Answer 3

a)(689+875)+125=689+(875+125)=689+1000=1689

581 + (878+419)=581+419+878=1000+878=1878

b)(2/7+4/9)+5/7=2/7+5/7+4/9=7/7+4/9=1+4/9=9/9+4/9=13/9

17/11+(7/15+5/11)=17/11+5/11+7/15=2+7/15=30/15+7/15=3/15

c)5,87+28,69+4,13=5,87+4,13+28,69=10+28,69=38,69

83,75+46,98+6,25=83,75+6,25+46,98=90+46,98=136,98

Answer 4

a) (689+875)+125=1553+125=1678

581+(878+419)=581+1297=1878

b) (\(\dfrac{2}{7}\)+\(\dfrac{4}{9}\))+\(\dfrac{5}{7}\)=(\(\dfrac{18}{63}\)+\(\dfrac{28}{63}\))+\(\dfrac{45}{63}\)=\(\dfrac{46}{63}\)+\(\dfrac{45}{63}\)=\(\dfrac{13}{9}\)

\(\dfrac{17}{11}\)+(\(\dfrac{7}{15}\)+\(\dfrac{5}{11}\))=\(\dfrac{17}{11}\)+\(\dfrac{5}{11}\)+\(\dfrac{7}{15}\)=2+\(\dfrac{7}{15}\)=\(\dfrac{37}{15}\)

c)5,87+28,69+4,13=38,69

83,75+46,98+6,25=136,98