(1)用7g+2g的砝码称出9g盐,140g-9g=131g
(2)用7g+2g砝码把131g盐分成两部分61g,70g (61+2+7=70)
(3)用2g砝码和9g盐把61g盐分成50g和11g两部分(61-9-2=11,11+50=61).11g+9g+70g=90g
(1)用7g+2g的砝码称出9g盐,140g-9g=131g
(2)用7g+2g砝码把131g盐分成两部分61g,70g (61+2+7=70)
(3)用2g砝码和9g盐把61g盐分成50g和11g两部分(61-9-2=11,11+50=61).11g+9g+70g=90g