① ﹣( ﹣ )
② ﹣( + )
③ + +
④ ﹣( + )
⑤ ﹣ ﹣
⑥ + + +
①
②
③
④
⑤
⑥54.3×1.8+54.3×0.3﹣54.3×0.1
0.75+ = 1- =
1- = 0.22=
学生讨论用了多长时间?