In the beginning, Martha lost 18 / 2 = <<18/2=9>>9 crayons.

So after she bought a set of new crayons, she has in total 9 + 20 = <<9+20=29>>29 crayons.

# Answer

29
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Martha has 18 crayons. She lost half of them, so she bought a new set of 20 crayons. How many crayons in total does Martha have after the purchase?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
29
Martha has 18 crayons. She lost half of them, so she bought a new set of 20 crayons. How many crayons in total does Martha have after the purchase?
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