<s>[INST] When I was four, my sister was half my age. Now I am 28, how old is my sister? [/INST] Your sister is 26 years old.</s>\ <s>[INST] That is correct. Can you explain how you came to the right conclusion? [/INST] 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.</s>