Answer:
1. 
(one decimal place.)
2.
(two decimal places.)
3. 
(three significant figures.)
Explanation:
<h3>1.</h3>
The first and second expressions are additions and subtractions. When adding two numbers, the accuracy of the result is given by the number of decimal places in it. The result should have as many decimal places as the input with the least number of decimal places.
For example, in the first expression:
has four decimal places.
has only one decimal place.
has two decimal places.
Therefore, the result should be rounded to one decimal place. Note that these units are compatible for addition, since they are all the same. The result should have the same unit (that is: 
.)
Therefore:
. (Rounded to one decimal place.)
<h3>2.</h3>
Similarly:
has two decimal places.
has four decimal places.
Therefore, the result should be rounded to two decimal places. Its unit should be 
(same as the unit of the two inputs.)
. (Rounded to two decimal places.)
<h3>3.</h3>
When multiplying two numbers, the accuracy of the result should be based on the number of significant figures in it. The result should have as many significant figures as the input with the least number of significant figures. In this expression:
has three significant figures.
has five significant figures.
Therefore, the result should have only three significant figures.
The unit of the result is supposed to be the product of the units of the input. In this expression, that unit will be 
, which is occasionally written as 
.
. (Rounded to three significant figures.)
