2．下面各题，怎样简便就怎样算
| $\frac{2}{3}$+$\frac{4}{15}$×$\frac{5}{8}$ | $\frac{3}{85}$×86 | $\frac{12}{17}$×$\frac{5}{12}$×17 | $\frac{5}{16}$×$\frac{8}{15}$-$\frac{1}{18}$ |
| $\frac{5}{7}$×$\frac{4}{15}$×$\frac{7}{8}$ | $\frac{1}{6}$×$\frac{3}{8}$×$\frac{6}{11}$ | （$\frac{7}{9}$+$\frac{5}{27}$）×54 | $\frac{5}{6}$×$\frac{7}{8}$+$\frac{5}{6}$×$\frac{1}{8}$ |
1．口算
| $\frac{5}{9}$×15= | $\frac{3}{5}$×2= | $\frac{1}{4}$×$\frac{4}{5}$= | $\frac{1}{9}$×$\frac{3}{7}$= | $\frac{7}{12}$×$\frac{3}{4}$= |
| 1×$\frac{3}{20}$= | $\frac{2}{5}$×$\frac{15}{4}$= | $\frac{4}{17}$×34= | $\frac{8}{21}$×$\frac{7}{16}$= | $\frac{1}{20}$×$\frac{2}{3}$= |
18．自然数可以分成（ ）
0 153667 153675 153681 153685 153691 153693 153697 153703 153705 153711 153717 153721 153723 153727 153733 153735 153741 153745 153747 153751 153753 153757 153759 153761 153762 153763 153765 153766 153767 153769 153771 153775 153777 153781 153783 153787 153793 153795 153801 153805 153807 153811 153817 153823 153825 153831 153835 153837 153843 153847 153853 153861 199269
| A． | 偶数和奇数 | B． | 质数和合数 | C． | 因数和倍数 |