John buys 100 shares of stock at $100 per share. The price goes up by 10% and he sells 50 shares. Then, prices drop by 10% and he sells his remaining 50 shares. How much does he get for the last 50?

The stock first increases by 10% => Each share value is added with $10, which is equal to $110 per share.
Then, the price decreases by %10 of $110 which is equal to $11. So, the sale price is $110-$11 = $99 per share.
Therefore, the sale price for 50 shares was 99 x $50 = $4950.