diff --git a/_concepts.txt b/_concepts.txt
index 5c96c53..4cdd4a1 100644
--- a/_concepts.txt
+++ b/_concepts.txt
@@ -69,3 +69,7 @@ def concept ninety as 90
 ninety isa number
 def concept nineties from bnf ninety number where number < 10 as ninety + number
 nineties isa number
+def concept hundreds from number1 hundred and number2 where number1 < 10 and number2 < 100 as number1 * 100 + number2
+def concept one hundred as 100
+one hundred isa number
+hundreds is number