Môn Toán Lớp 4: 4/20+9/30+16/40+25/50+36/60+49/70+64/80+81/90

$\dfrac{4}{20}+\dfrac{9}{30}+\dfrac{16}{40}+\dfrac{25}{50}+\dfrac{36}{60}+\dfrac{49}{70}+\dfrac{64}{80}+\dfrac{81}{90}$

$=\dfrac{1}{5}+\dfrac{3}{10}+\dfrac{2}{5}+\dfrac{1}{2}+\dfrac{3}{5}+\dfrac{7}{10}+\dfrac{4}{5}+\dfrac{9}{10}$

$=\dfrac{10}{5}+\dfrac{3}{10}+\dfrac{1}{2}+\dfrac{7}{10}+\dfrac{9}{10}$

$=\dfrac{10}{5}+\dfrac{19}{10}+\dfrac{1}{2}$

$=\dfrac{20}{10}+\dfrac{19}{10}+\dfrac{5}{10}$

$=\dfrac{20+19+5}{10}$ $=\dfrac{44}{10}$

$=\dfrac{22}{5}$