To find out how many rubber duckies are on the cover of this book you could count each one—or you could estimate. An estimate is a good guess. Are there more than ten rubber ducks? Are there fewer than a thousand?

Those estimates are not very accurate. A great estimate is close to the real number. Filled with fun, creative examples, this companion to Great Estimations will show you how to train your eyes and your mind to make really great estimations about length, volume, area, and much more.