解方程．（最后一题要验算）（1）6x﹣0.9=4.5（2）12x﹣9x=8.7（3）3（x+2.1）=10.5．
0.8+0.55+1.2-0.45
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口算。+=-=+=-+= 0.63×1000= 0. 75-0.25= 0.07+0.03= 0. 9÷0.03= 0.4×0.8=
×=÷3=÷=－= 3÷15=＋0.25= 1÷= 85%－15%= 10÷10%= 5×÷5×=
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