(ただし1と2を合せて12のような使い方は出来ません。)
20個の解法が見つかりました。
((3+(9-1))-1)=10
((3+9)-(1+1))=10
((3-(1-9))-1)=10
((3-1)+(9-1))=10
((3-1)-(1-9))=10
((9+(3-1))-1)=10
((9-(1-3))-1)=10
((9-1)+(3-1))=10
((9-1)-(1-3))=10
(3+((9-1)-1))=10
(3+(9-(1+1)))=10
(3-((1+1)-9))=10
(3-(1+(1-9)))=10
(3-(1-(9-1)))=10
(9+((3-1)-1))=10
(9+(3-(1+1)))=10
(9-((1+1)-3))=10
(9-(1+(1-3)))=10
(9-(1-(3-1)))=10