The number of baseball cards in Neil's collection is 80 percent of the number in Larry's collection. If Neil has 80 fewer baseball cards than Larry, how many do they have altogether

N=L (80/100)

N=0.8L

...

N=L-80

Since N=N

0.8L=L-80 subtract 0.8L from both sides

0=0.2L-80 add 80 to both sides

80=0.2L divide both sides by 0.2

400=L, and since N=L-80

N=320

N+L=400+320

So they have 720 baseball cards altogether.