#### Answer

a. 1 g

#### Work Step by Step

A thick paperback book with hundreds of pages could weigh approximately 1 kg. Since a dollar bill is much lighter than a whole book, clearly 1 kg and 4 kg are too heavy as estimates for the weight of a dollar bill.
If a paperback book with 500 pages weighs 1 kg (which is 1000 grams), then each page weighs about 2 grams. A dollar bill seems like it would be a bit lighter than a single page from a paperback book, so 1 gram is a good estimate for the weight of a dollar bill.
The best estimate for the weight of a dollar bill is 1 gram.