分析:(1)根據(jù)比的基本性質(zhì)作答,即比的前項(xiàng)和后項(xiàng)同時(shí)乘一個(gè)數(shù)或除以一個(gè)數(shù)(0除外)比值不變.
(2)先換算成統(tǒng)一單位,再化簡(jiǎn);
(3)根據(jù)比的基本性質(zhì)作答,即比的前項(xiàng)和后項(xiàng)同時(shí)乘一個(gè)數(shù)或除以一個(gè)數(shù)(0除外)比值不變.
解答:解:(1)51:34,
=(51÷17):(34÷17),
=3:2;
(2)
噸:750千克,
=(
×1000)千克:750千克,
=125:750,
=1:6;
(3)5.6:4.2,
=(56×10):(4.2×10),
=56:42,
=(56÷7):(42÷7),
=8:6,
=(8÷2):(6÷2),
=4:3.
點(diǎn)評(píng):此題主要考查了化簡(jiǎn)比的方法,注意化簡(jiǎn)比時(shí),比的兩項(xiàng)的單位一定要統(tǒng)一;化簡(jiǎn)比的結(jié)果是一個(gè)比,它的前項(xiàng)和后項(xiàng)都是整數(shù),并且是互質(zhì)數(shù).