diff --git a/main.py b/main.py
index d123f96..3cc1799 100755
--- a/main.py
+++ b/main.py
@@ -169,8 +169,7 @@ for r in res:
 	t = tokenizer.replace_variables(tokens, list(r))
 	#tokenizer.print_token_list(t)
 	result = calc_engine.calculate_results(t)
-	tol = int(exp.wrong_response * tolerance + exp.wrong_response) 
-	if result <= tol and result >= int(exp.wrong_response - exp.wrong_response * tolerance):
+	if result <= int(exp.wrong_response(1 + tolerance)) and result >= int(exp.wrong_response(1 - tolerance)):
 		if not result in answers:
 			answers[result]	 = t
 	#if result <= tol and result >= int(exp.wrong_response - exp.wrong_response * tolerance):
diff --git a/tokenizer.py b/tokenizer.py
index 774ff31..ca4c4bf 100644
--- a/tokenizer.py
+++ b/tokenizer.py
@@ -44,6 +44,12 @@ def get_tokens_from_expression_string(expression_string):
 				#Must be a variable.
 				if tokens[-1].type == token.TokenType.exp_start:
 					variable_is_negative = True
+				elif token.TokenType.get_operator(tokens[-1].value) != token.TokenType.unknown:
+					variable_is_negative = True
+				elif tokens[-1].type == token.TokenType.exp_end:
+					tokens.append(token.Token(c, token.TokenType.get_operator(c)))
+					parsing_number = False
+					tmp = ""
 			else:
 				tokens.append(token.Token(c, token.TokenType.get_operator(c)))
 				parsing_number = False