1. 直接写出得数。(6分)
2020+80= 2.8+8.2= 4.52+5.8-2.8=
2-70%= 365-99= 3.8×99+3.8=
$\frac{2}{3}-\frac{1}{12}= 25%×4= 2-\frac{2}{3}+\frac{1}{3}=$
$\frac{8}{9}×15= 36÷1.2= \frac{3}{5}×10÷\frac{3}{5}×10=$
答案：1. 2100 11 7.52 1.3 266 380 $\frac{7}{12}$ 1 $\frac{5}{3}$(或1$\frac{2}{3}$) $\frac{40}{3}$ 30 100
解析：
2100；11；7.52；1.3；266；380；$\frac{7}{12}$；1；$\frac{5}{3}$；$\frac{40}{3}$；30；100
2. 计算下面各题,能简算的要简算。(12分)
15×30-618÷6 13.92÷2.4+44÷10 25×3.2×125
$\frac{25}{49}×\frac{1}{12}+\frac{23}{49}÷12 (\frac{1}{4}+\frac{3}{7})×7×4 \frac{3}{4}÷[(\frac{4}{5}+\frac{1}{4})×\frac{3}{7}]$
答案：2. 347 10.2 10000 $\frac{4}{49}$ 19 $\frac{5}{3}$
解析：
15×30-618÷6
=450-103
=347
13.92÷2.4+44÷10
=5.8+4.4
=10.2
25×3.2×125
=25×0.4×8×125
=(25×0.4)×(8×125)
=10×1000
=10000
$\frac{25}{49}×\frac{1}{12}+\frac{23}{49}÷12$
=$\frac{25}{49}×\frac{1}{12}+\frac{23}{49}×\frac{1}{12}$
=$(\frac{25}{49}+\frac{23}{49})×\frac{1}{12}$
=$\frac{48}{49}×\frac{1}{12}$
=$\frac{4}{49}$
$(\frac{1}{4}+\frac{3}{7})×7×4$
=$\frac{1}{4}×7×4+\frac{3}{7}×7×4$
=7+12
=19
$\frac{3}{4}÷[(\frac{4}{5}+\frac{1}{4})×\frac{3}{7}]$
=$\frac{3}{4}÷[(\frac{16}{20}+\frac{5}{20})×\frac{3}{7}]$
=$\frac{3}{4}÷[\frac{21}{20}×\frac{3}{7}]$
=$\frac{3}{4}÷\frac{9}{20}$
=$\frac{3}{4}×\frac{20}{9}$
=$\frac{5}{3}$
3. 解方程或解比例。(6分)
$\frac{2}{3}x-\frac{1}{4}x=\frac{5}{8} \frac{5}{7}:x=4:\frac{7}{15} 0.5x+3.5=5.2$
答案：3. x=$\frac{3}{2}$ x=$\frac{1}{12}$ x=3.4
解析：
$\frac{2}{3}x - \frac{1}{4}x = \frac{5}{8}$
解：$\frac{8}{12}x - \frac{3}{12}x = \frac{5}{8}$
$\frac{5}{12}x = \frac{5}{8}$
$x = \frac{5}{8} ÷ \frac{5}{12}$
$x = \frac{5}{8} × \frac{12}{5}$
$x = \frac{3}{2}$
$\frac{5}{7}:x = 4:\frac{7}{15}$
解：$4x = \frac{5}{7} × \frac{7}{15}$
$4x = \frac{1}{3}$
$x = \frac{1}{3} ÷ 4$
$x = \frac{1}{12}$
$0.5x + 3.5 = 5.2$
解：$0.5x = 5.2 - 3.5$
$0.5x = 1.7$
$x = 1.7 ÷ 0.5$
$x = 3.4$
