\(a,\dfrac{2}{5}+\dfrac{3}{8}+\dfrac{4}{5}+\dfrac{7}{8}=\left(\dfrac{2}{5}+\dfrac{4}{5}\right)+\left(\dfrac{3}{8}+\dfrac{7}{8}\right)=\dfrac{6}{5}+\dfrac{5}{4}=\dfrac{24}{20}+\dfrac{25}{20}=\dfrac{49}{20}\)
\(b,\dfrac{5}{6}+\dfrac{4}{15}+\dfrac{3}{5}+\dfrac{7}{6}=\left(\dfrac{5}{6}+\dfrac{7}{6}\right)+\left(\dfrac{4}{15}+\dfrac{3}{5}\right)=2+\dfrac{4}{5}=\dfrac{10}{5}+\dfrac{4}{5}=\dfrac{14}{5}\)
\(\dfrac{4}{13}+\left(\dfrac{7}{13}+\dfrac{3}{4}\right)+\dfrac{3}{8}=\left(\dfrac{4}{13}+\dfrac{7}{13}\right)+\left(\dfrac{3}{4}+\dfrac{3}{8}\right)=\dfrac{11}{13}+\dfrac{9}{8}=\dfrac{205}{104}\)
a)\(=\left(\dfrac{2}{5}+\dfrac{4}{5}\right)+\left(\dfrac{7}{8}+\dfrac{3}{8}=\dfrac{6}{4}+\dfrac{10}{8}=\dfrac{6}{4}+\dfrac{5}{4}=\dfrac{11}{4}\right)\)
b)\(=\left(\dfrac{5}{6}+\dfrac{7}{6}\right)+\left(\dfrac{4}{15}+\dfrac{3}{5}\right)=\dfrac{12}{6}+\dfrac{13}{15}=\dfrac{30}{15}+\dfrac{13}{15}=\dfrac{43}{15}\)
c)\(=\left(\dfrac{4}{13}+\dfrac{7}{13}\right)+\left(\dfrac{3}{4}+\dfrac{3}{8}\right)=\dfrac{11}{13}+\left(\dfrac{6}{8}+\dfrac{3}{8}\right)=\dfrac{11}{13}+\dfrac{9}{8}=\dfrac{205}{104}\)
=(2/5+4/5)+(3/8+7/8)=6/5+10/8=49/20
=(5/6+7/6)+4/15+3/5=(2+13/15)=43/15
=4/13+7/13+3/4+3/8=(4/13+7/13)+(3/4+3/8)=11/13+9/8=250/104=125/52
^^
a) 2/5 + 3/8 + 4/5 + 7/8
= (2/5 + 4/5) + (3/8 + 7/8)
= 6/5 + 5/4
= 49/20
