\(1,\dfrac{12}{25}+\dfrac{3}{5}+\dfrac{13}{25}=\left(\dfrac{12}{25}+\dfrac{13}{25}\right)+\dfrac{3}{5}=1+\dfrac{3}{5}=\dfrac{8}{5}\\ 2,\dfrac{3}{2}+\dfrac{2}{3}+\dfrac{4}{3}=\dfrac{3}{2}+\left(\dfrac{2}{3}+\dfrac{4}{3}\right)=\dfrac{3}{2}+2=\dfrac{7}{2}\\ 3,\dfrac{3}{2}+\dfrac{7}{5}+\dfrac{3}{4}=\left(\dfrac{3}{2}+\dfrac{3}{4}\right)+\dfrac{7}{5}=\left(\dfrac{6}{4}+\dfrac{3}{4}\right)+\dfrac{7}{5}=\dfrac{9}{4}+\dfrac{7}{5}=\dfrac{45}{20}+\dfrac{28}{20}=\dfrac{73}{20}\)
Quy đồng 3/5 cho cùng mẫu chung là 25 có
12/25+15/25+13/25=40/25=8/5
Mẫu chung là 6 có
9/6+4/6+8/6=21/6=7/2
Quy đồng mẫu chung là 20 có
30/20+28/30+15/20=73/20
Chúc em học tốt
12/25 + 3/5 + 13/25 = (12/25 +13/25) + 3/5 = 1 + 3/5 = 8/5
3/2 + 2/3 + 4/3 =3/2 + ( 2/3+4/3 ) = 7/2
3/2 + 7/5 + 3/4 = ( 3/2+3/4) + 7/5 = 12/5
