Barry bought 21. He gave 3/7 of them to his sister. How many stamps did he have left?

Barry bought 21 stamps. He gave his sister 3/7 of them. How many does he have left?

21 stamps = 7/7. Sister has 3/7 of them. Barry has what fraction?

Well, what do you think, show us some work. This is a very easy question since both 3 and 7 divide into 21. 3/7 X 21=. Start there