How many significant figures are in -20.0?

Answer 1

Three (3).

Rules for significant figures:

1. Leading zeros are never significant. Leading zeros are ones that come before any other digit, such as the first 0 in 0.1

2. Non-zero digits are always significant.

3. Zeros between two non-zero digits are always significant. In 202, the 0 is significant because of this.

4. Trailing zeros are significant if and only if there is a decimal point. For example, 200 has 1 significant figure, but 200. has 3.