Answer:
PLEASE TAKE YOUR TIME AND THINK THROUGH EVERY PROBLEM. USE THE C.U.B.E.S STRATEGY WHEN NEEDED.
Step-by-step explanation:
  
        
             
        
        
        
1/5 full =250g
4/5 full =550g
550g-250g=300g=3/5 without jug
1/5 without jug=300g/3=100g
250g-100g=150g
<u>The jug weighs 150g empty</u>
        
                    
             
        
        
        
Answer: It is a difference of two squares, and it factors to (3x-7)(3x+7)
=============================================================
Explanation:
We can write the 9x^2 as (3x)^2 since
(3x)^2 = (3x)*(3x) = (3*3)*(x*x) = 9x^2
The 49 can be written as 7^2 because 7^2 = 7*7 = 49.
This means 9x^2 - 49 is the same as (3x)^2 - 7^2. We have a difference of two squares.
The difference of squares factoring rule is
a^2 - b^2 = (a-b)(a+b)
which we have a = 3x and b = 7 in this case
So,
a^2 - b^2 = (a-b)(a+b)
(3x)^2 - 7^2 = (3x-7)(3x+7)
9x^2 - 49 = (3x-7)(3x+7)
Side note: This is the same as (3x+7)(3x-7). We can multiply two numbers in any order.