Nancy, who graduated from State University in June 2013, 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, 2013, 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.