1/3 of 1200 is 400, because 1200 divided by 3 is 400. So she gives 400 to her sister, which means she has 1200-400= 800 left. When she gives 1/4 of the remaining to her brother, that means that we need to figure out how much 1/4 of 800 is. 800 divided by 4 is 200. So Katie gives 200 to her brother.
800 that she has remaining minus the 200 she gives to her brother leaves her with 800-200 = 600
