1. 直接写出得数。
$60×\frac {3}{4}=$ $\frac {2}{7}÷\frac {1}{4}=$ $\frac {2}{3}÷\frac {1}{2}+\frac {2}{3}=$
$\frac {5}{6}×\frac {6}{7}=$ $\frac {7}{8}÷\frac {13}{16}=$ $\frac {7}{8}÷14=$
$\frac {1}{8}×\frac {1}{9}=$ $\frac {4}{5}÷\frac {1}{5}+\frac {2}{3}=$ $160÷\frac {4}{5}=$
$7\frac {2}{15}×5=$ $16\frac {7}{8}÷2=$ $\frac {1}{4}+\frac {1}{4}÷\frac {1}{4}=$

$60×\frac {3}{4}=15×3=45$
$\frac {2}{7}÷\frac {1}{4}=\frac {2}{7}×4=\frac {8}{7}$
$\frac {2}{3}÷\frac {1}{2}+\frac {2}{3}=\frac {4}{3}+\frac {2}{3}=2$
$\frac {5}{6}×\frac {6}{7}=\frac {5}{7}$
$\frac {7}{8}÷\frac {13}{16}=\frac {7}{8}×\frac {16}{13}=\frac {14}{13}$
$\frac {7}{8}÷14=\frac {7}{8}×\frac {1}{14}=\frac {1}{16}$
$\frac {1}{8}×\frac {1}{9}=\frac {1}{72}$
$\frac {4}{5}÷\frac {1}{5}+\frac {2}{3}=4+\frac {2}{3}=4\frac {2}{3}$
$160÷\frac {4}{5}=160×\frac {5}{4}=200$
$7\frac {2}{15}×5=7×5+\frac {2}{15}×5=35+\frac {2}{3}=35\frac {2}{3}$
$16\frac {7}{8}÷2=16÷2+\frac {7}{8}÷2=8+\frac {7}{16}=8\frac {7}{16}$
$\frac {1}{4}+\frac {1}{4}÷\frac {1}{4}=\frac {1}{4}+1=1\frac {1}{4}$

2. 选出正确的选项。
(1)把 20 g 药放入 200 g 水中,药和药水的比是()。
A. $1:10$ B. $1:11$ C. $10:1$ D. $11:1$
(2)一个等腰三角形,若一个底角与顶角度数的比是$2:1$,则这个等腰三角形也是()。
A. 钝角三角形 B. 直角三角形 C. 锐角三角形 D. 无法确定
(3)一项工程,计划 5 h 完成,实际 4 h 就完成了任务,工作效率提高了()。
A. $\frac {1}{20}$ B. $\frac {1}{5}$ C. $\frac {1}{4}$ D. 无法确定

(1)
20:(20+200)=1:11
选B
(2)
180÷(2+2+1)=36
36×2=72
选C
(3)
$(\frac{1}{4}-\frac{1}{5})÷\frac{1}{5}=\frac{1}{4}$
选C

3. 脱式计算。(能简算的要简算)
$1.25×2.5×32$ $(27+\frac {18}{19})÷9$

$1.25×2.5×32$
$=1.25×2.5×(8×4)$
$=(1.25×8)×(2.5×4)$
$=10×10$
$=100$
$(27+\frac {18}{19})÷9$
$=(27+\frac {18}{19})×\frac {1}{9}$
$=27×\frac {1}{9}+\frac {18}{19}×\frac {1}{9}$
$=3+\frac {2}{19}$
$=3\frac {2}{19}$

4. 解方程。
$5x-4.5×2=0.5$ $x÷(1-60\%)=1.15$

解：
5x - 4.5×2 = 0.5
5x - 9 = 0.5
5x = 0.5 + 9
5x = 9.5
x = 9.5 ÷ 5
x = 1.9
解：
x÷(1-60%) = 1.15
x÷0.4 = 1.15
x = 1.15×0.4
x = 0.46