Ferran has to sell 20 buttons to raise money for the art club. He sold 1/2 of the buttons to her neighbors and 1/2 of the remainder to his friends. How many buttons did Ferran have left to sell?
sell 1/2 ....then 1/2 left
1/2 left sell 1/2 then 1/4 left
1/4 * 20 = 5 left to sell
+1223 start: 20 buttons
1/2 sold to neighbors: 10 buttons
1/2 of the remainder = 1/2 * (1 - 1/2) = 1/4 ---> 5 buttons
buttons left = 20 - 10 - 5 = 5 buttons
