You have the 175 on the wrong line, the problem says 175 feet from the base, this is the bottom of the tree.
See attached picture for solution:
9+8 is the commutative property
480 pennies.
25% are dated before 1980, therefore:
1200(total):100 = 12 (1%)
12(1%)x25 = 300 (25%)
35% are dated from 1980 to 2000, therefore:
12(1%)x35 = 420 (35%)
25% are dated before 1980, 35% are dated from 1980 to 2000 and the rest are dated after 2000.
25% + 35% = 60%.
300(25%) + 420(35%) = 720.
60% = 720.
100%-60% = 40%.
40% is the amount of pennies that are dated after 2000.
The total (100%) of the pennies is 1200.
We also know that 60% of the total (1200) is 720.
1200(100%) - 720(60%) = 480(40%).
Therefore, the amount of pennies dated after 2000 in Russell’s Collection is 480.
