Eighty percent of a roof, or 2800 square feet of the roof, has been re-shingled. What is the total area of the roof?
A 35,000 sq ft
B 22.400 sq ft
C 3500 sq ft
D 2240 sq ft

a) 35,000 sq ft

Step-by-step explanation:

x = total area

the question is: 80% of what number equals 2800

.8x = 2800

x = 2800/0.8

x = 3500

step-by-step explanation:

1. practice, practice & more practice

2. review errors

3. master the key concepts

do not try to memorise the processes.

4. understand your doubts.

5. create a distraction free study environment

6. create a mathematical dictionary

7. apply maths to real world problems.

let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.