1、使用加减乘除、括号的话,有45个算式：(5+5-5)*5-5=20,(5+5)*(5+5)/5=20,5+5*5-(5+5)=20,5+5*5-5-5=20 (5+5)/5*(5+5)=20,(5+5)/(5/(5+5))=20,5-(5+5)+5*5=20,5-(5+5-5*5)=20 5-5+5*5-5=20,(5-5+5)*5-5=20,5-5-5+5*5=20,5-5-(5-5*5)=20 5-(5-5*5+5)=20,5-(5-5*5)-5=20,(5-(5-5))*5-5=20,5-(5-(5*5-5))=20 5*5+5-(5+5)=20,5*5+5-5-5=20,5*(5+5-5)-5=20,5*5-(5+5)+5=20 5*5-5+5-5=20,5*(5-5+5)-5=20,5*5-(5+5-5)=20,5*5-5-5+5=20 5*5-(5-5+5)=20,5*5-(5-5)-5=20,5*5-5-(5-5)=20,5*(5-(5-5))-5=20 5*5-(5-(5-5))=20,5*5-5*5/5=20,(5*5-5)*5/5=20,5*5-5/5*5=20 (5*5-5)/5*5=20,5*5-5/(5/5)=20,(5*5-5)/(5/5)=20,5*(5*5-5)/5=20 5*5*5/5-5=20,5*5/5*5-5=20,5*5/(5/5)-5=20,5/5*5*5-5=20 5/5*(5*5-5)=20,5/(5/5)*5-5=20,5/(5/(5*5))-5=20,5/(5/(5*5-5))=20 5/(5/5/5)-5=20
2、如果加减乘除必须全部使用的话,无解.
3、如果可以使用乘方,有55个(5+5-5)*5-5=20,(5+5)*(5+5)/5=20,5+5*5-(5+5)=20,5+5*5-5-5=20 (5+5)/5*(5+5)=20,(5+5)/(5/(5+5))=20,5-(5+5)+5*5=20,5-(5+5-5*5)=20 5-5+5*5-5=20,(5-5+5)*5-5=20,5-5-5+5*5=20,5-5-(5-5*5)=20 5-(5-5*5+5)=20,5-(5-5*5)-5=20,(5-(5-5))*5-5=20,5-(5-(5*5-5))=20 (5-(5/5)^5)*5=20,(5-5^(5-5))*5=20,5*5+5-(5+5)=20,5*5+5-5-5=20 5*(5+5-5)-5=20,5*5-(5+5)+5=20,5*5-5+5-5=20,5*(5-5+5)-5=20 5*5-(5+5-5)=20,5*5-5-5+5=20,5*5-(5-5+5)=20,5*5-(5-5)-5=20 5*5-5-(5-5)=20,5*(5-(5-5))-5=20,5*5-(5-(5-5))=20,5*5-5*5/5=20 (5*5-5)*5/5=20,5*5-5/5*5=20,(5*5-5)/5*5=20,5*5-5/(5/5)=20 (5*5-5)/(5/5)=20,5*(5-(5/5)^5)=20,5*(5-5^(5-5))=20,5*5-5^(5/5)=20 (5*5-5)^(5/5)=20,5*(5*5-5)/5=20,5*5*5/5-5=20,5*5/5*5-5=20 5*5/(5/5)-5=20,5*5^(5/5)-5=20,(5*5)^(5/5)-5=20,5/5*5*5-5=20 5/5*(5*5-5)=20,5/(5/5)*5-5=20,5/(5/(5*5))-5=20,5/(5/(5*5-5))=20 5/(5/5/5)-5=20,5^((5+5)/5)-5=20,5^(5/5)*5-5=20
真的,我发现没得解,不信你试试