Question

 tính :

a)  2/5 + 3/4 =               7/12 - 2/7 + 1/12 =                          12/17 - 5/17 - 4/17

b) 675,39 + 342,14 =             563 , 87 + 403 , 13 =        

Answer 1

a) \(\frac{2}{3}+\frac{3}{4}=\frac{8}{12}+\frac{9}{12}=\frac{17}{12}\)

\(\frac{7}{12}-\frac{2}{7}+\frac{1}{12}=\frac{7}{12}+\left(-\frac{2}{7}\right)+\frac{1}{12}=\frac{7}{12}+\frac{1}{12}+\left(-\frac{2}{7}\right)=\frac{8}{12}+\left(-\frac{2}{7}\right)=\frac{2}{3}+\left(-\frac{2}{7}\right)=-\left(\frac{14}{21}+\frac{6}{21}\right)=-\frac{20}{21}\)

\(\frac{12}{17}-\frac{5}{17}-\frac{4}{17}=\frac{12-5-4}{17}=\frac{3}{17}\)

b) 675,39 + 342,14 = 1017,53

563,87 + 403,13 = 967

Answer 2

a]2/3+3/4=8/12+9/12=17/12

7/12-2/7+1/12=49/84-24/84+7/84=25/84+7/84=32/84=8/21

12/17-5/17-4/7=7/17-4/17=3/17
b]675,39+342,14=999,53

563,87+403,13=967