Ali made some bookmarks to sell at a funfair. He sold 50 bookmarks on Saturday and 1/3 of the remaining bookmarks on Sunday. He still had 3/7 of the bookmarks left. How many bookmarks did Ali make?

B - 50 - (B - 50)(1/3) = (3/7)B

B - 50 - (1/3)B+ 50/3 = (3/7)B

(2/3)B -100/3 = (3/7)B

(2/3 - 3/7)B = 100/3

(5/21)B = 100/3

B = (100/3) ( 21/5) = (100 / 5) ( 21 / 3) = 20 * 7 = 140 = total that he made