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1.直接写出得数。
(1)$\frac{1}{5}+\frac{1}{2}=$ $\frac{1}{2}-\frac{1}{4}=$ $\frac{1}{8}+\frac{1}{9}=$
$\frac{1}{4}-\frac{1}{8}=$ $\frac{7}{10}-\frac{1}{5}=$ $\frac{1}{12}-\frac{1}{15}=$
$\frac{1}{18}+\frac{1}{13}=$ $\frac{1}{2}+\frac{1}{3}=$ $\frac{1}{9}-\frac{1}{10}=$
(2)$2.5×4×6=$ $6×4×5=$ $2.5×8×5=$
$10×10×5=$ $0.5×0.3×3=$ $3.5×2×3=$
$2.5×8×3=$ $0.8×0.5×3=$ $10×10×7=$
(1)$\frac{1}{5}+\frac{1}{2}=$ $\frac{1}{2}-\frac{1}{4}=$ $\frac{1}{8}+\frac{1}{9}=$
$\frac{1}{4}-\frac{1}{8}=$ $\frac{7}{10}-\frac{1}{5}=$ $\frac{1}{12}-\frac{1}{15}=$
$\frac{1}{18}+\frac{1}{13}=$ $\frac{1}{2}+\frac{1}{3}=$ $\frac{1}{9}-\frac{1}{10}=$
(2)$2.5×4×6=$ $6×4×5=$ $2.5×8×5=$
$10×10×5=$ $0.5×0.3×3=$ $3.5×2×3=$
$2.5×8×3=$ $0.8×0.5×3=$ $10×10×7=$
答案
(1)
$\frac{1}{5}+\frac{1}{2}=\frac{2}{10}+\frac{5}{10}=\frac{7}{10}$
$\frac{1}{2}-\frac{1}{4}=\frac{2}{4}-\frac{1}{4}=\frac{1}{4}$
$\frac{1}{8}+\frac{1}{9}=\frac{9}{72}+\frac{8}{72}=\frac{17}{72}$
$\frac{1}{4}-\frac{1}{8}=\frac{2}{8}-\frac{1}{8}=\frac{1}{8}$
$\frac{7}{10}-\frac{1}{5}=\frac{7}{10}-\frac{2}{10}=\frac{1}{2}$
$\frac{1}{12}-\frac{1}{15}=\frac{5}{60}-\frac{4}{60}=\frac{1}{60}$
$\frac{1}{18}+\frac{1}{13}=\frac{13}{234}+\frac{18}{234}=\frac{31}{234}$
$\frac{1}{2}+\frac{1}{3}=\frac{3}{6}+\frac{2}{6}=\frac{5}{6}$
$\frac{1}{9}-\frac{1}{10}=\frac{10}{90}-\frac{9}{90}=\frac{1}{90}$
(2)
$2.5×4×6=10×6=60$
$6×4×5=24×5=120$
$2.5×8×5=20×5=100$
$10×10×5=100×5=500$
$0.5×0.3×3=0.15×3=0.45$
$3.5×2×3=7×3=21$
$2.5×8×3=20×3=60$
$0.8×0.5×3=0.4×3=1.2$
$10×10×7=100×7=700$
$\frac{1}{5}+\frac{1}{2}=\frac{2}{10}+\frac{5}{10}=\frac{7}{10}$
$\frac{1}{2}-\frac{1}{4}=\frac{2}{4}-\frac{1}{4}=\frac{1}{4}$
$\frac{1}{8}+\frac{1}{9}=\frac{9}{72}+\frac{8}{72}=\frac{17}{72}$
$\frac{1}{4}-\frac{1}{8}=\frac{2}{8}-\frac{1}{8}=\frac{1}{8}$
$\frac{7}{10}-\frac{1}{5}=\frac{7}{10}-\frac{2}{10}=\frac{1}{2}$
$\frac{1}{12}-\frac{1}{15}=\frac{5}{60}-\frac{4}{60}=\frac{1}{60}$
$\frac{1}{18}+\frac{1}{13}=\frac{13}{234}+\frac{18}{234}=\frac{31}{234}$
$\frac{1}{2}+\frac{1}{3}=\frac{3}{6}+\frac{2}{6}=\frac{5}{6}$
$\frac{1}{9}-\frac{1}{10}=\frac{10}{90}-\frac{9}{90}=\frac{1}{90}$
(2)
$2.5×4×6=10×6=60$
$6×4×5=24×5=120$
$2.5×8×5=20×5=100$
$10×10×5=100×5=500$
$0.5×0.3×3=0.15×3=0.45$
$3.5×2×3=7×3=21$
$2.5×8×3=20×3=60$
$0.8×0.5×3=0.4×3=1.2$
$10×10×7=100×7=700$
2.脱式计算。
$1-\frac{5}{8}+\frac{2}{8}$ $\frac{11}{12}-\frac{1}{12}-\frac{1}{6}$ $\frac{5}{6}-\frac{1}{18}-\frac{2}{9}$
$\frac{3}{14}+\frac{2}{7}-\frac{1}{14}$ $2-\frac{9}{14}-\frac{5}{14}$ $3-\frac{1}{6}-\frac{1}{12}$
$1-\frac{1}{3}-\frac{1}{3}$ $\frac{9}{13}-\frac{4}{13}-\frac{5}{13}$ $\frac{4}{5}+\frac{1}{2}+\frac{1}{5}$
$\frac{7}{9}+\frac{2}{3}+\frac{2}{9}$ $\frac{6}{5}-\frac{2}{3}-\frac{1}{5}$ $\frac{7}{15}-\frac{1}{5}+\frac{8}{15}$
$1-\frac{5}{8}+\frac{2}{8}$ $\frac{11}{12}-\frac{1}{12}-\frac{1}{6}$ $\frac{5}{6}-\frac{1}{18}-\frac{2}{9}$
$\frac{3}{14}+\frac{2}{7}-\frac{1}{14}$ $2-\frac{9}{14}-\frac{5}{14}$ $3-\frac{1}{6}-\frac{1}{12}$
$1-\frac{1}{3}-\frac{1}{3}$ $\frac{9}{13}-\frac{4}{13}-\frac{5}{13}$ $\frac{4}{5}+\frac{1}{2}+\frac{1}{5}$
$\frac{7}{9}+\frac{2}{3}+\frac{2}{9}$ $\frac{6}{5}-\frac{2}{3}-\frac{1}{5}$ $\frac{7}{15}-\frac{1}{5}+\frac{8}{15}$
答案
$1-\frac{5}{8}+\frac{2}{8}$
$=\frac{3}{8}+\frac{2}{8}$
$=\frac{5}{8}$
$\frac{11}{12}-\frac{1}{12}-\frac{1}{6}$
$=\frac{10}{12}-\frac{2}{12}$
$=\frac{8}{12}$
$=\frac{2}{3}$
$\frac{5}{6}-\frac{1}{18}-\frac{2}{9}$
$=\frac{15}{18}-\frac{1}{18}-\frac{4}{18}$
$=\frac{10}{18}$
$=\frac{5}{9}$
$\frac{3}{14}+\frac{2}{7}-\frac{1}{14}$
$=\frac{3}{14}-\frac{1}{14}+\frac{4}{14}$
$=\frac{2}{14}+\frac{4}{14}$
$=\frac{6}{14}$
$=\frac{3}{7}$
$2-\frac{9}{14}-\frac{5}{14}$
$=2-(\frac{9}{14}+\frac{5}{14})$
$=2-1$
$=1$
$3-\frac{1}{6}-\frac{1}{12}$
$=\frac{36}{12}-\frac{2}{12}-\frac{1}{12}$
$=\frac{33}{12}$
$=\frac{11}{4}$
$1-\frac{1}{3}-\frac{1}{3}$
$=1-(\frac{1}{3}+\frac{1}{3})$
$=1-\frac{2}{3}$
$=\frac{1}{3}$
$\frac{9}{13}-\frac{4}{13}-\frac{5}{13}$
$=\frac{5}{13}-\frac{5}{13}$
$=0$
$\frac{4}{5}+\frac{1}{2}+\frac{1}{5}$
$=\frac{4}{5}+\frac{1}{5}+\frac{1}{2}$
$=1+\frac{1}{2}$
$=\frac{3}{2}$
$\frac{7}{9}+\frac{2}{3}+\frac{2}{9}$
$=\frac{7}{9}+\frac{2}{9}+\frac{6}{9}$
$=1+\frac{6}{9}$
$=1+\frac{2}{3}$
$=\frac{5}{3}$
$\frac{6}{5}-\frac{2}{3}-\frac{1}{5}$
$=\frac{6}{5}-\frac{1}{5}-\frac{2}{3}$
$=1-\frac{2}{3}$
$=\frac{1}{3}$
$\frac{7}{15}-\frac{1}{5}+\frac{8}{15}$
$=\frac{7}{15}+\frac{8}{15}-\frac{3}{15}$
$=1-\frac{3}{15}$
$=1-\frac{1}{5}$
$=\frac{4}{5}$
$=\frac{3}{8}+\frac{2}{8}$
$=\frac{5}{8}$
$\frac{11}{12}-\frac{1}{12}-\frac{1}{6}$
$=\frac{10}{12}-\frac{2}{12}$
$=\frac{8}{12}$
$=\frac{2}{3}$
$\frac{5}{6}-\frac{1}{18}-\frac{2}{9}$
$=\frac{15}{18}-\frac{1}{18}-\frac{4}{18}$
$=\frac{10}{18}$
$=\frac{5}{9}$
$\frac{3}{14}+\frac{2}{7}-\frac{1}{14}$
$=\frac{3}{14}-\frac{1}{14}+\frac{4}{14}$
$=\frac{2}{14}+\frac{4}{14}$
$=\frac{6}{14}$
$=\frac{3}{7}$
$2-\frac{9}{14}-\frac{5}{14}$
$=2-(\frac{9}{14}+\frac{5}{14})$
$=2-1$
$=1$
$3-\frac{1}{6}-\frac{1}{12}$
$=\frac{36}{12}-\frac{2}{12}-\frac{1}{12}$
$=\frac{33}{12}$
$=\frac{11}{4}$
$1-\frac{1}{3}-\frac{1}{3}$
$=1-(\frac{1}{3}+\frac{1}{3})$
$=1-\frac{2}{3}$
$=\frac{1}{3}$
$\frac{9}{13}-\frac{4}{13}-\frac{5}{13}$
$=\frac{5}{13}-\frac{5}{13}$
$=0$
$\frac{4}{5}+\frac{1}{2}+\frac{1}{5}$
$=\frac{4}{5}+\frac{1}{5}+\frac{1}{2}$
$=1+\frac{1}{2}$
$=\frac{3}{2}$
$\frac{7}{9}+\frac{2}{3}+\frac{2}{9}$
$=\frac{7}{9}+\frac{2}{9}+\frac{6}{9}$
$=1+\frac{6}{9}$
$=1+\frac{2}{3}$
$=\frac{5}{3}$
$\frac{6}{5}-\frac{2}{3}-\frac{1}{5}$
$=\frac{6}{5}-\frac{1}{5}-\frac{2}{3}$
$=1-\frac{2}{3}$
$=\frac{1}{3}$
$\frac{7}{15}-\frac{1}{5}+\frac{8}{15}$
$=\frac{7}{15}+\frac{8}{15}-\frac{3}{15}$
$=1-\frac{3}{15}$
$=1-\frac{1}{5}$
$=\frac{4}{5}$
