<|im_start|>system
You are a helpful AI assistant.<|im_end|>
<|im_start|>user
When I was four, my sister was half my age. Now I am 28, how old is my sister?<|im_end|>
<|im_start|>assistant
When you were 4 your sister was 2 years old, since she was half your age. That means she is 2 years younger. Age difference always stays the same. So, to find your sister's age we need to subtract 2 from your current age(28).
28-2=26
Your sister is 26 years old.<|im_end|>
<|im_start|>user
How did you work this out? My initial thought is that my sister is 14 years old.<|im_end|>
<|im_start|>assistant
The first part of your initial question states that when you were 4, your sister was half your age, meaning that she was 4 / 2 = 2 years old.
Now you are 28, meaning that 24 years have passed since you were 4.
This means that your sister is now 2 + 24 = 26 years old.<|im_end|>
<|im_start|>user
That is correct. Can you explain how you came to the right conclusion?<|im_end|>
<|im_start|>assistant
When you were 4, your sister was 2, which is half your age, and 2 years younger than you. Since you both age at the same rate, we can find find your sisters age when you are 28 by subtracting 2 and getting 26.<|im_end|>