diff --git a/python-open-source-challenge/issue-17.py b/python-open-source-challenge/issue-17.py
index 73c6048..f3128ff 100644
--- a/python-open-source-challenge/issue-17.py
+++ b/python-open-source-challenge/issue-17.py
@@ -19,7 +19,7 @@ def summarize_orders(orders):
         quantity = order["quantity"]
         price = order["price"]
         # TODO: Check how each line contributes to the bill.
-        total += price
+        total += price * quantity
         # TODO: Check how repeated item orders are combined.
         quantities[item] = quantities.get(item, 0) + quantity
     # TODO: Check how an empty order list is handled.
diff --git a/python-open-source-challenge/issue-32.py b/python-open-source-challenge/issue-32.py
index 8b4646f..f492362 100644
--- a/python-open-source-challenge/issue-32.py
+++ b/python-open-source-challenge/issue-32.py
@@ -16,11 +16,11 @@ def subject_extremes(students):
     for student in students:
         for subject, mark in student["marks"].items():
             # TODO: Check how both ends of the subject range are initialized.
-            bounds = subjects.setdefault(subject, [0, mark])
+            bounds = subjects.setdefault(subject, [mark, mark])
             # TODO: Check how a new high mark updates the range.
-            bounds[0] = min(bounds[0], mark)
+            bounds[0] = max(bounds[0], mark)
             # TODO: Check how a new low mark updates the range.
-            bounds[1] = max(bounds[1], mark)
+            bounds[1] = min(bounds[1], mark)
     # TODO: Check the order and meaning of each returned bound.
     return subjects
 
diff --git a/python-open-source-challenge/issue-57.py b/python-open-source-challenge/issue-57.py
index 3a7a355..fb0a1a7 100644
--- a/python-open-source-challenge/issue-57.py
+++ b/python-open-source-challenge/issue-57.py
@@ -20,7 +20,7 @@ def mobile_charges(usages):
         # TODO: Check the data charge included in each record.
         cost += usage["data_gb"] * 2
         # TODO: Check how multiple records for one user are accumulated.
-        charges[user] = charges.get(user, 0) - cost
+        charges[user] = charges.get(user, 0) + cost
     # TODO: Check that users with no usage aren't fabricated.
     return charges
 
diff --git a/python-open-source-challenge/issue-74.py b/python-open-source-challenge/issue-74.py
index a70948d..676472f 100644
--- a/python-open-source-challenge/issue-74.py
+++ b/python-open-source-challenge/issue-74.py
@@ -23,7 +23,7 @@ def attendance_report(records, minimum_percent):
             present[student] = present.get(student, 0) + 1
     percentages = {student: present.get(student, 0) / total * 100 for student, total in counted.items()}
     # TODO: Check which students fall below the requested threshold.
-    below = [student for student, percent in percentages.items() if percent > minimum_percent]
+    below = [student for student, percent in percentages.items() if percent < minimum_percent]
     # TODO: Check that percentages for all students are returned.
     return percentages, below