一堆水管,从下到上一层比一层少1根堆放,下层放了13根,上层放了5根,一共放了9层,这堆水管共有 根.
×= ÷=0.2× =25× =1.
12个是 ,27×=27÷ × .
4×= ÷3= = = = =
×= ÷=0.5× =15× =1.
50的是18的.