<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] You state that at the age of 4 you're sister was half you're age. So 4 divided by 2 is 2, therefore she is 2 years younger than you. If you are now 28, then she is 26.</s>