diff --git a/docs/1b/ece124.md b/docs/1b/ece124.md
index 30ce76d..8c98a42 100644
--- a/docs/1b/ece124.md
+++ b/docs/1b/ece124.md
@@ -284,6 +284,15 @@ Each 1 square is effectively a minterm, and finding the least number of rectangl
 
 A K-map for five variables can be expressed in two maps for four variables — one with the fifth variable set to zero, and the other set to 1.
 
+### Multiplexers
+
+An $n$-input mux has $\lceil\log_2 n\rceil$ **select inputs** all in the same mux.
+
+!!! example
+    A 4-1 multiplexer. $f=s_0's_1A+s_0's_1B+s_0s_1'C+s_0s_1D$
+    
+    <img src="https://upload.wikimedia.org/wikipedia/commons/7/75/Multiplexer_4-to-1.svg" width=300>(Source: Wikimedia Commons)</img>
+
 ## VHDL
 
 VHDL is a hardware schematic language.
@@ -307,3 +316,4 @@ architecture LogicFunc of two_one_mux is
 In this case, the inputs are `a0, s, a1` that lead to an output `y`. All input/output is of type `bit` (a boolean).
 
 The **architecture** defines how inputs translate to outputs via functions. These all run **concurrently**.
+