###Human: James earns $10 per week as an allowance. After saving all his money for four weeks, he spends half of it on a new video game. He then spends a quarter of what is left to buy a new book. How much money does he have left?, ### Assistant: He starts out with $10 * 4 = $40.
James spend $40 / 2 = $20 on the video game.
After buying the game, he has $40 - $20 = $20 left.
He spent $20 / 4 = $5 on the book.
He has $20 - $5 = $15 left. 
 So the answer is :  15