Answer: 25 books. you can buy 25 books with 5 dollars
Step-by-step explanation:
Yep!
Weighing #1: Start off by splitting the pile of 12 coins evenly into two piles, 6 in each pile. Put one pile on each side of the balance. The side that is weighed down has the fake coin it in. Ignore the other 6 coins.
Weighing #2: Now you have 6 coins left. Split the pile evenly again, 3 in each pile. Repeat the same process and put each pile on one side of the balance. The side that is weighed down has your fake coin in it. Ignore the other 3 coins.
Weighing #3: You have 3 coins left. Take two coins, whichever two you like, and weigh them. If they weigh the same, then the one you didn't weigh is the fake one. If one is heavier, then that heavier one is your fake coin.
If you notice the picture below, the amount of fencing, or perimeter, that will be used will be 3w + 2l
now

solve for "w", to see what critical points you get, and then run a first-derivative test on them, for the minimum
notice the

so. you can pretty much skip that one, though is a valid critical point, the width can't clearly be 0
so.. check the critical points on the other
Use a protracter :) hope this helps!
Answer:
x = 11/7
Step-by-step explanation:
x - 2/7 = 9/7
x = 9/7 + 2/7
x = 11/7