Chapter 9, Problem 19A

In each of the following exercises, the value on the left must be multiplied by one of the following numbers: 0.0001; 0.001; 0.01; 0.1; 10; 100; 1000; or 10,000 in order to obtain the value on the right of the equal sign. Determine the proper number.

19. $643\times \underset{\_}{}=0.643$