解:(1)0.25:x=7.5:15,
7.5x=0.25×15,
7.5x÷7.5=3.75÷7.5,
x=0.5;
(2)x:8=3:0.5,
0.5x=3×8,
0.5x÷0.5=24÷0.5,
x=48;
(3)8:x=
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:
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,
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x=8×
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,
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x÷
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=4÷
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,
x=
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;
(4)6.5:x=3.25:4,
3.25x=6.5×4,
3.25x÷3.125=26÷3.25,
x=8.
分析:(1)根據(jù)比例的基本性質(zhì),兩內(nèi)項(xiàng)之積等于兩外項(xiàng)之積,將原式變形為7.5x=0.25×15,再根據(jù)等式的性質(zhì),兩邊同時(shí)除以7.5即可.
(2)根據(jù)比例的基本性質(zhì),兩內(nèi)項(xiàng)之積等于兩外項(xiàng)之積,將原式變形為0.5x=3×8,再根據(jù)等式的性質(zhì),兩邊同時(shí)除以0.5即可.
(3)根據(jù)比例的基本性質(zhì),兩內(nèi)項(xiàng)之積等于兩外項(xiàng)之積,將原式變形為
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x=8×
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,再根據(jù)等式的性質(zhì),兩邊同時(shí)除以
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即可.
(4)根據(jù)比例的基本性質(zhì),兩內(nèi)項(xiàng)之積等于兩外項(xiàng)之積,將原式變形為3.25x=6.5×4,再根據(jù)等式的性質(zhì),兩邊同時(shí)除以3.25即可.
點(diǎn)評(píng):此題考查了利用比例的基本性質(zhì)和等式的性質(zhì)解比例的方法的靈活應(yīng)用.注意等號(hào)對(duì)齊.