Step-by-step explanation:
You should always use the least number of significant figures.  The exception is exact numbers or constants.
For example, there are 60 minutes in an hour.  Even though this number has one significant figure, it is an exact number.  So 15 minutes converted to hours would be 0.25 hr.
 
        
             
        
        
        
Explanation:
Pair 1 is true if Jeff's monthly income is $600/20% = $3,000.
Pair 2 is true if Jeff's monthly income is $1200/10% = $12,000.
Both pairs can be true if Jeff's monthly income increased by a factor of 4 in the 20 years from 1990 to 2010.
Obviously, Jeff spent more on housing in 2010. (Fortunately for Jeff, that larger expenditure was a smaller fraction of his income.)
 
        
             
        
        
        
Answer:
2over/a -b-c
Step-by-step explanation:
 remove the parentheses