Nancy, who graduated from State University in June 2010, has just landed her first real job. She is excited because her salary is \(\$ 4,000\) per month. Nancy is single and has been planning all month about how she will spend her \(\$ 4,000\). When she received her first paycheck on June 30, 2010 , she was very disappointed. The amount of her check was only \(\$ 3,100\). Explain to Nancy why (generally) her check was not for \(\$ 4,000\).