Bob has a bag full of dimes and quarters. He has 20 coins worth $3.80. Which system of
equations could be used to determine the
number of dimes, d, and the number of
quarters, q, in Bob's bag?

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.