一列火车以同一速度驶过两个隧道，第一个隧道长420米，用了27秒钟；第二个隧道长480米，用了30秒钟。求这列火车每秒钟行驶多少米，火车长多少米？
直接写出得数+=÷= 12×=×= 21÷﹣84=﹣×= 10﹣=×÷×=+÷2=+×=
直接写得数．×0×17=÷4÷=÷= 57×=﹣+=××= 1÷=（6+）×=﹣=+=
4÷=×6÷= 6×+6×=×= （+）×16= 1÷=×= 24%×5=
口算： （1）÷= 4﹣= 0÷（1+）= （2）﹣= 1.75+=××12= （3）2×=÷= 2×（+）=×÷×=
直接写出得数．=== 6.3×10%== 7×== 40%﹣0.25=
+
=
÷
= 12×
=
×
=
﹣84=
﹣
×
= 10﹣
=
×
÷
×
+
÷2=
+
×
=
×0×17=
÷4÷
÷
= 57×
=
﹣
+
=
×
×
= 1÷
=（6+
）×
=
﹣
=
+
=
=
×6÷
+6×
=
×
=
+
）×16= 1÷
=
×
= 24%×5=
÷
= 4﹣
= 0÷（1+
）=
= 1.75+
=
×
×12=
=
÷
= 2×（
+
）=
×
÷
=
=
= 6.3×10%=
= 7×
=
= 40%﹣0.25=
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