Russell has a collection of 1,200 pennies. Of these pennies, 25% are dated before 1980, 35% are dated from 1980 to 2000, and the rest are dated after 2000. How many pennies in Russell’s collection are dated after 2000?

Plz help, I think I'm overthinking it.

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.