#### Answer

Significant figures contain all of the certain digits and the first uncertain digit (the first estimated digit) of a number.
This is how to write 1000 in different significant figures:
- 1 significant figure: 1000 or 1 × $10^{3}$
- 2 significant figures: 1.0 × $10^{3}$
- 3 significant figures: 1.00 × $10^{3}$
- 4 significant figures: 1000. or 1.000 × $10^{3}$
The answer cant be 1.0 since 1.0 has 2 significant figures while the actual answer (which is 1) has only 1 significant figure.

#### Work Step by Step

Significant figures contain all of the certain digits and the first uncertain digit (the first estimated digit) of a number.
To perform the calculation for the following operation $$\frac{1.5-1.0}{0.50} $$
We first have to consider the addition/subtraction significant figure rule. It is applied to 1.5 −1.0. The result of this is 0.5, which is a one significant figure answer.
Next, the multiplication/division rule is applied to 0.5/0.50. A one significant figure number divided by a two significant figure number yields an answer with one significant figure. The answer should therefore be 1.