由题意得,
(1/2)菜地+(1/3)麦地=13(公顷)...(1)
(1/3)菜地+(1/2)麦地=12(公顷)...(2)
将上述两式相加,即(1)+(2),得
[(1/2)菜地+(1/3)麦地]+[(1/3)菜地+(1/2)麦地]=13+12
(1/2)菜地+(1/3)麦地+(1/3)菜地+(1/2)麦地=25
整理,得
(1/2)菜地+(1/3)菜地+(1/3)麦地+(1/2)麦地=25
(5/6)菜地+(5/6)麦地=25
(5/6)(菜地+麦地)=25
菜地+麦地=25*(6/5)
菜地+麦地=30(公顷)
那么,(1/3)[菜地+麦地]=10(公顷)
即:(1/3)菜地+(1/3)麦地=10(公顷)...(3)
用(1)式减去(3)式,得
[(1/2)菜地+(1/3)麦地]-[(1/3)菜地+(1/3)麦地]=13-10
(1/2)菜地+(1/3)麦地-(1/3)菜地-(1/3)麦地=3
整理,得
(1/2)菜地-(1/3)菜地+(1/3)麦地-(1/3)麦地=3
(1/6)菜地=3
菜地=3*6
菜地=18(公顷)