Hannah = (1/2) 18 = 9

9 + 18 = <<9+18=27>>27 km

Together they walked 27 kilometers.

# Answer

27
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Nadia walked 18 kilometers, which was twice as far as Hannah walked. How many kilometers did the two girls walk in total?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
27
Nadia walked 18 kilometers, which was twice as far as Hannah walked. How many kilometers did the two girls walk in total?
train