Answer:
13 quarters must be tails.
Step-by-step explanation:
Number of quarters = 40% of 50 coins
Number of quarters = 40/100 * 50 = 20 coins which are quarters.
35% of these 20 quarters on heads. We can proceed in 2 ways from here.
We can actually find the number of quarters that are on heads.
35/100 * 20 = 7 quarters are showing heads.
Since the other quarters must be tails 20 - 7 = 13 quarters must be tails.
The other way to do it is to realize that if 35% of the coins are heads, 65% of the coins must be tails 20 * 65/100 = 13 which is a bit more direct.
