stripParentheses = Function[, StringReplace["(" | ")" | " " -> ""] @
    ToString[Unevaluated @ #, InputForm], HoldFirst];

stripParentheses[3*2 + 2/4*10]

ops = {"/", "*", "+"};

split = StringSplit[stripParentheses[3*2 + 2/4*10], a : Alternatives @@ ops :> a]

parenthesize = SequenceReplace[#, {a_, #2, b_} :> StringJoin["(",a,#2,b,")"]]&;


{StringJoin @ #, ToExpression @ StringJoin @ #} & @
  Fold[parenthesize, split, #] & /@ Permutations[ops] // 
 Grid[#, Dividers -> All] &

stripParentheses = Function[, StringReplace["(" | ")" | " " -> ""] @
    ToString[Unevaluated @ #, InputForm], HoldFirst];

stripParentheses[3*2 + 2/4*10]

ops = {"/", "*", "+"};

split = StringSplit[stripParentheses[3*2 + 2/4*10], a : Alternatives @@ ops :> a]

parenthesize = SequenceReplace[#, {a_, #2, b_} :> StringJoin["(",a,#2,b,")"]]&;


Map[{#, ## & @@ {StringJoin @ #, ToExpression @ StringJoin @ #} & @
   Fold[parenthesize, split, #]} &] @ Permutations[ops] // 
 Grid[#, Dividers -> All] &