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第58页

信息发布者：

$\begin{aligned}解：\frac {5}{8}x&=21×\frac {5}{14}\\\frac {5}{8}x&=\frac {15}{2}\\x&=12\end{aligned}$

$\begin{aligned}解：\frac {2}{3}x&=\frac {2}{9}×21\\\frac {2}{3}x&=\frac {14}{3}\\x&=7\end{aligned}$

=(772+128)-(317+283)

=900-600

=300

=0.4×(3×4×0.25)

=0.4×3×1

=1.2

=2.9×0.5

=1.45

$=5+\frac {12}{19}+\frac {7}{19}$

$=5+1$

$=6$

$=\frac {3}{4}×(127-26-1)$

$=\frac {3}{4}×100$

$=75$

$=1-\frac {1}{2}+\frac {1}{2}-\frac {1}{3}+...+\frac {1}{6}-\frac {1}{7}$

$=1-\frac {1}{7}$

$=\frac {6}{7}$

(4,5)