The age difference between Beth and her sister is 18 - 5 = <<18-5=13>>13 years.

Beth must be 13 x 2 = <<13*2=26>>26 to be twice her sister's age.

Beth will be twice her sister's age in 26 - 18 = <<26-18=8>>8 years.

# Answer

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<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If Beth is 18 years old and her little sister is 5, in how many years would she be twice her sister's age?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
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If Beth is 18 years old and her little sister is 5, in how many years would she be twice her sister's age?
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