Officials at the United States Mint believe that the Sacagawea dollar coin will be used as a substitute for four quarters more than for the dollar bill because it weighs only 8.1 grams, far less than four quarters, which weigh 5.67 grams each.
这个是答案,我有点搞不懂的是far less than前面是逗号, 要不要加is变成 is far less than?