###Human: A vendor at the market is selling sunglasses for $30 each. He has to spend a certain amount to buy these sunglasses. He sells 10 pairs in a day. He then takes half his profits and uses it to buy a new sign, which costs $20. How much does each pair of sunglasses cost him to buy?, ### Assistant: His profits were $40 because 20 / .5 = 40
He made $300 selling sunglasses because 10 x 30 = 300
His costs for the sunglasses were $260 because 300 - 40 = 260
The sunglasses cost him $26 each because 260 / 10 = 26 
 So the answer is :  26