第105页 - 亮点给力提优课时作业本五年级数学江苏版

$1 - \frac{3} {8} - \frac{3} {10} = \frac{13} {40}$

$答：还剩下宣纸总量的\frac {13}{40}.$

$10分=\frac{1}{6}时$

$\ \frac{1} {3}+\frac{1} {6}=\frac{1} {2}(时)$

$\ 2÷8=\frac{1}{4}\ $

$1 - \frac{1} {2} - \frac{1} {4} = \frac{1} {4}$

$答：剩下的路程占全程的\frac {1}{4}$

2

$\frac{2}{9}$

$1-{\frac{2018} {2021}} = {\frac{3} {2021}}\ $

$1-{\frac{2020} {2023}} = {\frac{3} {2023}}\ $

$1-{\frac{2022} {2025}} = \frac{3} {2025}$

$\ 因为\frac{3} {2021} ＞ \frac{3} {2023} ＞ \frac{3} {2025},$

$所以\frac{2018} {2021}＜\frac{2020} {2023} ＜ \frac{2022} {2025}。$

$100÷2+1=51(棵) ，51×2=102(棵)\ $

$51÷ (2+1)=17(组)\ $

$香樟树:17×2×2=68(棵)，68÷102=\frac{2}{3}\ $

$梧桐树:17×1×2=34(棵)，34÷102=\frac{1}{3}$

$答：香樟树占\frac {2}{3}，梧桐树占\frac {1}{3}。$

$\frac{48} {49}$

$\frac{4}{9}$

$2△4=\frac {1}{2}+\frac {1}{4}=\frac {3}{4}$

$(2△4)○(\frac {2}{3}+\frac {1}{5})$

$=\frac {3}{4}○(\frac {2}{3}+\frac {1}{5})$

$=(\frac {2}{3}+\frac {1}{5})-\frac {3}{4}$

$=\frac {7}{60}$