$\frac{2}{5}+\frac{4}{7}+\frac{1}{2}$=$(\frac{2}{5}+\frac{4}{7})+\frac{1}{2}$=$(\frac{14}{35}+\frac{20}{35})+\frac{1}{2}=\frac{34}{35}+\frac{1}{2}=\frac{68}{70}+\frac{35}{70}=\frac{103}{70}$
$\frac{9}{5}-\frac{3}{10}-\frac{2}{3}=(\frac{18}{10}-\frac{3}{10})-\frac{2}{3}=\frac{15}{10}-\frac{2}{3}=\frac{45}{30}-\frac{20}{30}=\frac{25}{10}=\frac{5}{2}$

$\frac{6}{5}+\frac{1}{2}-\frac{1}{5}=(\frac{12}{10}+\frac{5}{10})-\frac{1}{5}=\frac{15}{10}-\frac{1}{5}=\frac{15}{10}-\frac{2}{10}=\frac{13}{10}$

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2/5 + 4/7 + 1/2
= 14/35 + 20/35 + 1/2
= 34/35 + 1/2
= 68/70 + 35/70
= 103/70

9/5 - 3/10 - 2/3
= 18/10 - 3/10 - 2/3
= 15/10 - 2/3
= 45/30 - 20/30
= 25/30 = 5/6

6/5 + 1/2 - 1/5
= 12/10 + 5/10 - 1/5
= 17/10 - 1/5
= 17/10 - 2/10
= 15/10 = 3/2

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