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小5算数 分数のたし算ひき算8

小数と分数にチャレンジ!

帯分数に通分,今回は小数も混ざった問題が出てきます。

めざせ!分数マスター!

<問題>

次の①~④の計算をしよう!

① \(\displaystyle 1\frac{1}{3}+\frac{3}{4}=\)

② \(\displaystyle \frac{8}{15}-\frac{1}{3}=\)

③ \(\displaystyle 2\frac{1}{3}-\frac{9}{4}=\)

④ \(\displaystyle \frac{3}{5}+0.3=\)

正解はこちら!

① \(\displaystyle 1\frac{1}{3}+\frac{3}{4}\)

\(\displaystyle =1\frac{1×4}{3×4}+\frac{3×3}{4×3}\)

\(\displaystyle =1\frac{4}{12}+\frac{9}{12}\)

\(\displaystyle =1\frac{13}{12}\)

\(\displaystyle =2\frac{1}{12}\)

② \(\displaystyle \frac{8}{15}-\frac{1}{3}\)

\(\displaystyle =\frac{8}{15}-\frac{1×5}{3×5}\)

\(\displaystyle =\frac{8}{15}-\frac{5}{15}\)

\(\displaystyle =\frac{3}{15}\)

\(\displaystyle =\frac{1}{5}\)

③ \(\displaystyle 2\frac{1}{3}-\frac{9}{4}\)

この問題,ひき算でのくり下げがたいへん!

\(\displaystyle =2\frac{1×4}{3×4}-\frac{9×3}{4×3}\)

\(\displaystyle =2\frac{4}{12}-\frac{27}{12}\)

\(\displaystyle =1\frac{4+12}{12}-\frac{27}{12}\)

\(\displaystyle =\frac{4+12+12}{12}-\frac{27}{12}\)

\(\displaystyle =\frac{28}{12}-\frac{27}{12}\)

\(\displaystyle =\frac{1}{12}\)

④ \(\displaystyle \frac{3}{5}+0.3\)

0.1は\(\displaystyle \frac{1}{10}\)だから,0.3は\(\displaystyle \frac{3}{10}\)だね!

\(\displaystyle =\frac{3}{5}+\frac{3}{10}\)

\(\displaystyle =\frac{3×2}{5×2}+\frac{3}{10}\)

\(\displaystyle =\frac{6}{10}+\frac{3}{10}\)

\(\displaystyle =\frac{9}{10}\)

全問正解できたかな?

③と④は難しめですが,ぜひチャレンジしてみてくださいね。