Answer:
Nathan’s estimate is reasonable. He spent about $300 and earned about $200 so he should have about $100 less than he started with.
Step-by-step explanation:
Lets use round #s
He buys 10 posters at $30 each, so he spent 10*30 = 300
He sells 5 posters at $40 each, so he made 5*40 = 200
So he made 200 - 300 = -100, meaning he made 100 less than he started with. 100 less from 1000 is $900.