Four chefs can cook a dish in twenty minutes. They hire an extra chef. How long will it take the five of them to cook the same dish, if they all work at the same rate as the original four?

When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. if you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term.