(ただし1と2を合せて12のような使い方は出来ません。)
21個の解法が見つかりました。
((5+7)+(7-9))=10
((5+7)-(9-7))=10
((5-9)+(7+7))=10
((7+(5+7))-9)=10
((7+7)+(5-9))=10
((7+7)-(9-5))=10
((7-9)+(5+7))=10
(5+((7+7)-9))=10
(5+(7+(7-9)))=10
(5+(7-(9-7)))=10
(5-((9-7)-7))=10
(5-(9-(7+7)))=10
(7+((5+7)-9))=10
(7+(5+(7-9)))=10
(7+(5-(9-7)))=10
(7+(7+(5-9)))=10
(7+(7-(9-5)))=10
(7-((9-5)-7))=10
(7-((9-7)-5))=10
(7-(9-(5+7)))=10