diff --git a/maths/area.py b/maths/area.py
new file mode 100644
index 0000000..bc271db
--- /dev/null
+++ b/maths/area.py
@@ -0,0 +1,16 @@
+def circle_area(radius: float) -> float:
+    """
+    >>> circle_area(10)
+    314.1592653589793
+    >>> circle_area(0)
+    0.0
+    """
+    import math
+
+    return math.pi * radius * radius
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
diff --git a/maths/leap_year.py b/maths/leap_year.py
new file mode 100644
index 0000000..99acff7
--- /dev/null
+++ b/maths/leap_year.py
@@ -0,0 +1,19 @@
+"""
+https://en.wikipedia.org/wiki/Leap_year
+"""
+
+
+def is_leap_year(year: int) -> bool:
+    """
+    >>> all(is_leap_year(year) for year in [1600, 2000, 24000])
+    True
+    >>> all(is_leap_year(year) for year in [1999, 2001, 2002])
+    False
+    """
+    return year % 4 == 0 and year % 100 != 0 or year % 400 == 0
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
diff --git a/maths/sum_to_n.py b/maths/sum_to_n.py
new file mode 100644
index 0000000..78f6cf9
--- /dev/null
+++ b/maths/sum_to_n.py
@@ -0,0 +1,14 @@
+def sum_to_n(n: int) -> int:
+    """
+    >>> sum_to_n(100)
+    5050
+    >>> sum_to_n(10)
+    55
+    """
+    return sum(i for i in range(1, n + 1))
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()