第29页 - 启东中学作业本七年级数学人教版

$(-\frac {14}{15})$

$(-\frac {3}{2})×(-\frac {38}{15})$

$\frac {19}{5}$

$=370×\frac {1}{4}+\frac {1}{4}×24\frac {1}{2}+5\frac {1}{2}×\frac {1}{4}$

$=\frac {1}{4}× (370+24\frac {1}{2}+5\frac {1}{2})$

$=\frac {1}{4}×400=100$

$=-(8×\frac {1}{8}×12×\frac {1}{3}×0.001)$

$=-0.004$

$=-5×(\frac {3}{13}-\frac {2}{13}+\frac {1}{13})+\frac {14}{13}$

$=-\frac {10}{13}+\frac {14}{13}$

$=\frac {4}{13}$

-33

解：$(1)$小军的解法较好

$(2)49 \frac {24}{25}×(-5)=(50-\frac {1}{25})×(-5)=50×(-5)-\frac {1}{25}×(-5)=-250+\frac {1}{5}=-249 \frac {4}{5}$

$(3)(-19 \frac {15}{16})×8=(-20+\frac {1}{16})×8=(-20)×8+\frac {1}{16}×8=-160+\frac {1}{2}=-159 \frac {1}{2}$

解：$(2)$原式$=(-12-1)+(-20-1)=-13-21=-34$

$(3)$新运算$“a※b=ab-1”$不满足对加法的分配律，例如：$(-4)※(3+5)≠(-4)※3+(-4)※5$