159+356+117=
*660-309-228=
700-207+359=
420+330=
578-200=
660+140=
818-178=
440-170=
562-142-110=
720+180-400=
305+195+162=
127+305+469
1000-220-418
517-339+426
①670-395=
②*600-253-127= 验算:
③635-(329+135)=
④238+421+147=