三、计算题。(共29分)
1. 直接写得数。(每题1分,共8分)
$\frac{1}{3}-\frac{1}{6}=$
$1÷\frac{4}{5}=$
$\frac{3}{4}×\frac{8}{9}=$
$\frac{1}{2}÷\frac{5}{7}=$
$5.8×9 + 5.8=$
$\frac{4}{5}-(\frac{4}{5}-\frac{1}{2})=$
$\frac{3}{8}+\frac{5}{8}-\frac{5}{8}+\frac{3}{8}=$
$\frac{4}{5}÷\frac{3}{5}÷\frac{3}{5}×\frac{4}{5}=$
1. 直接写得数。(每题1分,共8分)
$\frac{1}{3}-\frac{1}{6}=$
$1÷\frac{4}{5}=$
$\frac{3}{4}×\frac{8}{9}=$
$\frac{1}{2}÷\frac{5}{7}=$
$5.8×9 + 5.8=$
$\frac{4}{5}-(\frac{4}{5}-\frac{1}{2})=$
$\frac{3}{8}+\frac{5}{8}-\frac{5}{8}+\frac{3}{8}=$
$\frac{4}{5}÷\frac{3}{5}÷\frac{3}{5}×\frac{4}{5}=$
答案:
$\frac{1}{6}$,$\frac{5}{4}$,$\frac{2}{3}$,$\frac{7}{10}$,58,$\frac{1}{2}$,$\frac{3}{4}$,$\frac{16}{9}$
解析:
$\frac{1}{3}-\frac{1}{6}=\frac{2}{6}-\frac{1}{6}=\frac{1}{6}$
$1÷\frac{4}{5}=1×\frac{5}{4}=\frac{5}{4}$
$\frac{3}{4}×\frac{8}{9}=\frac{24}{36}=\frac{2}{3}$
$\frac{1}{2}÷\frac{5}{7}=\frac{1}{2}×\frac{7}{5}=\frac{7}{10}$
$5.8×9 + 5.8=5.8×(9 + 1)=58$
$\frac{4}{5}-(\frac{4}{5}-\frac{1}{2})=\frac{4}{5}-\frac{4}{5}+\frac{1}{2}=\frac{1}{2}$
$\frac{3}{8}+\frac{5}{8}-\frac{5}{8}+\frac{3}{8}=(\frac{3}{8}+\frac{3}{8})+(\frac{5}{8}-\frac{5}{8})=\frac{6}{8}=\frac{3}{4}$
$\frac{4}{5}÷\frac{3}{5}÷\frac{3}{5}×\frac{4}{5}=\frac{4}{5}×\frac{5}{3}×\frac{5}{3}×\frac{4}{5}=\frac{16}{9}$
解析:
$\frac{1}{3}-\frac{1}{6}=\frac{2}{6}-\frac{1}{6}=\frac{1}{6}$
$1÷\frac{4}{5}=1×\frac{5}{4}=\frac{5}{4}$
$\frac{3}{4}×\frac{8}{9}=\frac{24}{36}=\frac{2}{3}$
$\frac{1}{2}÷\frac{5}{7}=\frac{1}{2}×\frac{7}{5}=\frac{7}{10}$
$5.8×9 + 5.8=5.8×(9 + 1)=58$
$\frac{4}{5}-(\frac{4}{5}-\frac{1}{2})=\frac{4}{5}-\frac{4}{5}+\frac{1}{2}=\frac{1}{2}$
$\frac{3}{8}+\frac{5}{8}-\frac{5}{8}+\frac{3}{8}=(\frac{3}{8}+\frac{3}{8})+(\frac{5}{8}-\frac{5}{8})=\frac{6}{8}=\frac{3}{4}$
$\frac{4}{5}÷\frac{3}{5}÷\frac{3}{5}×\frac{4}{5}=\frac{4}{5}×\frac{5}{3}×\frac{5}{3}×\frac{4}{5}=\frac{16}{9}$
2. 计算下面各题,怎样简便就怎样算。(每题2分,共12分)
$\frac{4}{5}÷7×\frac{5}{9}$
$\frac{2}{15}×4÷\frac{7}{25}$
$\frac{1}{4}×\frac{13}{72}×\frac{4}{13}$
$15×\frac{1}{20}÷\frac{7}{8}$
$\frac{1}{5}÷\frac{1}{15}×\frac{5}{9}$
$9÷\frac{1}{16}÷18$
$\frac{4}{5}÷7×\frac{5}{9}$
$\frac{2}{15}×4÷\frac{7}{25}$
$\frac{1}{4}×\frac{13}{72}×\frac{4}{13}$
$15×\frac{1}{20}÷\frac{7}{8}$
$\frac{1}{5}÷\frac{1}{15}×\frac{5}{9}$
$9÷\frac{1}{16}÷18$
答案:
$\frac{4}{63}$,$\frac{40}{21}$,$\frac{1}{72}$,$\frac{6}{7}$,$\frac{5}{3}$,8
解析:
$\frac{4}{5}÷7×\frac{5}{9}=\frac{4}{5}×\frac{1}{7}×\frac{5}{9}=\frac{4}{63}$
$\frac{2}{15}×4÷\frac{7}{25}=\frac{8}{15}×\frac{25}{7}=\frac{40}{21}$
$\frac{1}{4}×\frac{13}{72}×\frac{4}{13}=\frac{1}{4}×\frac{4}{13}×\frac{13}{72}=\frac{1}{72}$
$15×\frac{1}{20}÷\frac{7}{8}=\frac{3}{4}×\frac{8}{7}=\frac{6}{7}$
$\frac{1}{5}÷\frac{1}{15}×\frac{5}{9}=3×\frac{5}{9}=\frac{5}{3}$
$9÷\frac{1}{16}÷18=9×16×\frac{1}{18}=8$
解析:
$\frac{4}{5}÷7×\frac{5}{9}=\frac{4}{5}×\frac{1}{7}×\frac{5}{9}=\frac{4}{63}$
$\frac{2}{15}×4÷\frac{7}{25}=\frac{8}{15}×\frac{25}{7}=\frac{40}{21}$
$\frac{1}{4}×\frac{13}{72}×\frac{4}{13}=\frac{1}{4}×\frac{4}{13}×\frac{13}{72}=\frac{1}{72}$
$15×\frac{1}{20}÷\frac{7}{8}=\frac{3}{4}×\frac{8}{7}=\frac{6}{7}$
$\frac{1}{5}÷\frac{1}{15}×\frac{5}{9}=3×\frac{5}{9}=\frac{5}{3}$
$9÷\frac{1}{16}÷18=9×16×\frac{1}{18}=8$
3. 解方程。(每题3分,共9分)
$5x - 4.2=8.8$
$\frac{2}{3}x+\frac{3}{5}x=38$
$6x + 5×4.4=40$
$5x - 4.2=8.8$
$\frac{2}{3}x+\frac{3}{5}x=38$
$6x + 5×4.4=40$
答案:
$x=2.6$,$x=30$,$x=3$
解析:
$5x - 4.2=8.8$
$5x=8.8 + 4.2$
$5x=13$
$x=2.6$
$\frac{2}{3}x+\frac{3}{5}x=38$
$\frac{10}{15}x+\frac{9}{15}x=38$
$\frac{19}{15}x=38$
$x=38×\frac{15}{19}$
$x=30$
$6x + 5×4.4=40$
$6x + 22=40$
$6x=18$
$x=3$
解析:
$5x - 4.2=8.8$
$5x=8.8 + 4.2$
$5x=13$
$x=2.6$
$\frac{2}{3}x+\frac{3}{5}x=38$
$\frac{10}{15}x+\frac{9}{15}x=38$
$\frac{19}{15}x=38$
$x=38×\frac{15}{19}$
$x=30$
$6x + 5×4.4=40$
$6x + 22=40$
$6x=18$
$x=3$
四、解决问题。(每题5分,共35分)
1. 1盆百合花的价钱是1盆玫瑰花价钱的2倍。妈妈买来3盆百合花和8盆玫瑰花,一共用去224元。1盆百合花和1盆玫瑰花各多少元?
1. 1盆百合花的价钱是1盆玫瑰花价钱的2倍。妈妈买来3盆百合花和8盆玫瑰花,一共用去224元。1盆百合花和1盆玫瑰花各多少元?
答案:
1盆玫瑰花16元,1盆百合花32元。
解析:设1盆玫瑰花$x$元,则百合花$2x$元,$3×2x+8x=224$,6x+8x=224,14x=224,x=16,百合花:2×16=32(元)。
解析:设1盆玫瑰花$x$元,则百合花$2x$元,$3×2x+8x=224$,6x+8x=224,14x=224,x=16,百合花:2×16=32(元)。
2. 学校买4张办公桌和9把椅子一共用去504元。已知一把椅子的价钱正好是一张办公桌价钱的$\frac{1}{3}$,一把椅子和一张办公桌各多少元?
答案:
一把椅子24元,一张办公桌72元。
解析:设一张办公桌$x$元,则椅子$\frac{1}{3}x$元,$4x+9×\frac{1}{3}x=504$,4x+3x=504,7x=504,x=72,椅子:$\frac{1}{3}×72=24$(元)。
解析:设一张办公桌$x$元,则椅子$\frac{1}{3}x$元,$4x+9×\frac{1}{3}x=504$,4x+3x=504,7x=504,x=72,椅子:$\frac{1}{3}×72=24$(元)。
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