Most quantities that we deal with every day depend on two or more other quantities. For example, the time it takes to roast a chicken depends on the temperature of the oven and the size (or mass) of the chicken. The larger the chicken the longer the time required to cook it. The hotter the oven, the less time required to cook it. In this section, the ideas of one variable functions-those with one dependent and one independent variable- are extended to functions which have several independent variables.