Answer:
250 cards
Step-by-step explanation:
Let the number of baseball cards he originally had be x.
He sold 20% of the baseball cards after week one. This means that after week one the number of cards he had was:
x - (20/100 * x) = x - 0.2x = 0.8x
During week two he bought 20% more cards than he had after week one. This means that after week two, he had:
0.8x + (20/100 * 0.8x)
= 0.8x + (0.2 * 0.8x)
= 0.8x + 0.16x = 0.96x
He now has 10 fewer cards. This means that:
x - 10 = 0.96x
Collecting like terms:
x - 0.96x = 10
0.04x = 10
=> x = 10/0.04 = 250
He had 250 cards originally.
