题目内容

化简比,并求比值.
3.5:0.9 2.5:10 720:9600 45分:1.5时
2.25:6.25 99:55 25cm:0.5m 4吨:25千克.
分析:(1)根据比的基本性质,即比的前项和后项同时乘或除以一个相同的数(0除外)比值不变,进而把比化成最简比;
(2)根据求比值的方法,就用最简比的前项除以后项即得比值.
解答:解:(1)3.5:0.9,
=(3.5×10):(0.9×10),
=35:9;
3.5:0.9,
=35:9,
=35÷9,
=
35
9


(2)2.5:10,
=(2.5×2):(10×2),
=5:20,
=1:4;
2.5:10,
=1:4,
=1÷4,
=
1
4


(3)720:9600,
=(720÷80):(9600÷80),
=9:120,
=3:40;
720:9600,
=3:40,
=3÷40,
=
3
40


(4)45分:1.5时,
=45分:90分,
=(45÷45):(90÷45),
=1:2;
45分:1.5时,
=1:2,
=1÷2,
=
1
2


(5)2.25:6.25,
=(2.25×:20):(6.25×20),
=45:125,
=9:25;
2.25:6.25,
=9:25,
=9÷25,
=
9
25


(6)99:55,
=(99÷11):(55÷11),
=9:5;
99:55,
=9:5,
=9÷5,
=
9
5


(7)25cm:0.5m,
=25cm:50cm,
=(25÷25)÷(50÷25),
=1:2;
25cm:0.5m,
=1:2,
=1÷2,
=
1
2


(8)4吨:25千克,
=4000千克:25千克,
=(4000÷25):(25÷25),
=160:1;
4吨:25千克,
=160:1,
=160÷1,
=160.
点评:此题考查化简比和求比值的方法,要注意区分:化简比的结果是一个比,而求比值的结果是一个数;还要注意:如果比的前后项是名数时,要把单位化统一后再化简比或求比值.
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