在1000米的直线跑道上，间距50米放一个障碍物，那么一共要放多少个障碍物？
找准对应．（12）
×15=÷=÷50%= 8×25%=×0×=﹣= 0.5+=×=÷3=（﹣）×30=
16÷0.25====== 1﹣= 2.25+×=====
直接写得数×8=×= 81÷=÷= 63÷=÷=××= 3×÷3×= 36×25%=（﹣）×24=
直接写出得数： 25×= 1.8×=÷=÷3=﹣=﹣=（+）×30=÷×=．
×15=
÷
=
÷50%= 8×25%=
×0×
=
﹣
= 0.5+
=
×
=
÷3=（
﹣
）×30=
=
=
=
=
= 1﹣
= 2.25+
×
=
=
=
=
=
×8=
×
= 81÷
=
÷
= 63÷
=
÷
=
×
×
= 3×
÷3×
﹣
）×24=
= 1.8×
=
÷
÷3=
﹣
=
﹣
=（
+
）×30=
÷
×
=．
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