diff --git a/homeworks/27_Yassen_Efremov/avg_brightness.py b/homeworks/27_Yassen_Efremov/avg_brightness.py
new file mode 100644
index 0000000..8924d79
--- /dev/null
+++ b/homeworks/27_Yassen_Efremov/avg_brightness.py
@@ -0,0 +1,57 @@
+# =============================================================================================== #
+# Classes, Functions, Global variables #
+
+
+def avg_recursive(matrix, cell_row, cell_col, avg_region_brightness):
+	avg_region_brightness.append(matrix[cell_row][cell_col])		# add the brightness of the current cell
+	matrix[cell_row][cell_col] = 0	# Mark the cell as visited
+	# Start calling the function recursively on all the neighboor cells
+	for i in range(-1, 2):
+		for j in range(-1, 2):
+			# Check if the next indexes are out of range
+			if (0 <= cell_row + i < len(matrix)) and (0 <= cell_col + j < len(matrix[0])):
+				# Check if the next cell has brightness 0 or is the current cell
+				if (matrix[cell_row + i][cell_col + j] != 0) and ([i, j] != [0, 0]):
+					avg_recursive(matrix, cell_row + i, cell_col + j, avg_region_brightness)		
+
+
+def avg_brightness(matrix):
+	matrix_copy = [list(matrix_inner) for matrix_inner in matrix]		# copy so that we don't modify the passed list
+	avg_brightnesses = []
+
+	# Look for cells with brightness above 0 and start recursively going through them
+	for i in range(0, len(matrix_copy)):
+		for j in range(0, len(matrix_copy[0])):
+			if matrix_copy[i][j] > 0:
+				avg_region_brightness = []
+				avg_recursive(matrix_copy, i, j, avg_region_brightness)
+				avg_brightnesses.append(avg_region_brightness)
+
+	avg_brightnesses.sort(key = lambda row: sum(row) / len(row), reverse=True)
+	for row in avg_brightnesses:
+		print(sum(row) / len(row))
+
+
+# =============================================================================================== #
+
+
+def main():
+
+	# Example
+	matrix = (
+		(170,   0,   0, 255, 221,   0),
+		( 68,   0,  17,   0,   0,  68),
+		(221,   0, 238, 136,   0, 255),
+		(  0,   0,  85,   0, 136, 238),
+		(238,  17,   0,  68,   0, 255),
+		( 85, 170,   0, 221,  17,   0)
+	)
+
+	avg_brightness(matrix)
+
+
+# =============================================================================================== #
+
+
+if __name__ == "__main__":
+	main()
diff --git a/homeworks/27_Yassen_Efremov/num_ways.py b/homeworks/27_Yassen_Efremov/num_ways.py
new file mode 100644
index 0000000..03c5d3b
--- /dev/null
+++ b/homeworks/27_Yassen_Efremov/num_ways.py
@@ -0,0 +1,46 @@
+import time
+
+
+# =============================================================================================== #
+# Classes, Functions, Global variables #
+
+
+def num_ways(N, found):
+	# Optimized with memoization
+
+	if N in found:
+		return found[N]
+
+	if N <= 1: return 1
+
+	num = num_ways(N - 1, found) + num_ways(N - 2, found)
+	found[N] = num
+
+	return num
+
+
+
+# =============================================================================================== #
+
+
+def main():
+
+	start_time = time.time()
+	dict = {}
+
+	# Examples
+	print("Ways to climb a ladder with {} steps: {}".format(2, num_ways(2, dict)))
+	print("Ways to climb a ladder with {} steps: {}".format(3, num_ways(3, dict)))
+	print("Ways to climb a ladder with {} steps: {}".format(5, num_ways(5, dict)))
+	print("Ways to climb a ladder with {} steps: {}".format(7, num_ways(7, dict)))
+
+	# print("Ways to climb a ladder with {} steps: {}".format(100, num_ways(200, dict)))
+
+	print("\n### Completed after {:.6f} seconds ###".format(time.time() - start_time))
+
+
+# =============================================================================================== #
+
+
+if __name__ == "__main__":
+	main()
diff --git a/homeworks/27_Yassen_Efremov/replace.py b/homeworks/27_Yassen_Efremov/replace.py
new file mode 100644
index 0000000..1b6dc7f
--- /dev/null
+++ b/homeworks/27_Yassen_Efremov/replace.py
@@ -0,0 +1,34 @@
+# =============================================================================================== #
+# Classes, Functions, Global variables #
+
+
+def replace(a_list, to_find, replace_with):
+	list_copy = list(a_list)	# copy so that we don't modify the passed list
+
+	for i, value in enumerate(list_copy):
+		if value == to_find:
+			# Found a value to replace
+			list_copy[i] = replace_with
+		elif type(value) in [list, tuple]:
+			# Found another collection => iterate through it recursively
+			list_copy[i] = replace(list_copy[i], to_find, replace_with)
+	
+	return list_copy
+
+
+# =============================================================================================== #
+
+
+def main():
+
+	# Examples
+	list = [ 'a', 1, [['a', 'b'], 1], ([1, 3, 'a'], 'b')]
+	res = replace(list, 'a', 'c')
+	print(res) # => [ 'c', 1, [ ['c', 'b'], 1], ([1, 3, 'c'], 'b')]
+
+
+# =============================================================================================== #
+
+
+if __name__ == "__main__":
+	main()