The number of books sold is 473.
<u>Step-by-step explanation:</u>
- The original cost of each book = $0.64
- The selling price of each book = $0.75
The difference between the original price and selling price of the book gives the profit per book.
The profit of one book = Selling price - Original price
Let,
- The total number of books be 'x'.
- The number of books sold be 'y'.
- The unsold books is 100.
- The total profit is -12 because it was gone to a loss of $12.
Therefore, the equation is formed as 
total Profit = 0.75y - 0.64x 
⇒ 0.75y - 0.64x = -12 --------(1)
Total books = sold books + unsold books
x = y + 100
⇒ x-y = 100  -------(2)
Substitute x= 100+y in the eq(1),
0.75y - 0.64(100+y) = -12
0.75y - 64 -0.64y = -12
0.11y = -12 +64 
y = 52 / 0.11
y = 472.7
y ≅ 473 
The number of book sold is 473 books.
The total number of books is (100+473) = 573 books.
 
 
        
             
        
        
        
You add +7 to both sides and then divide by 9 to get the x alone.
        
                    
             
        
        
        
Answer:
Step-by-step explanation:
this is confusing b/c they are asking about two trains traveling at differnt speeds, but.. if you put the speeds together and make one train... imaginary.. ofc... traveling at the speed of both trains combined... when will it be 50 miles from the station?
maybe you can solve that?   I'll solve it below.. but.. if you can.. try it now, on your own
below is my answer... don't look until you have solved yours :P
80+70= 150kph
when will this have traveled 50Km?
you may be able to see that it will take 1/3 of an hour to travel 50 km
so 60 minutes times 1/3 = 20 minutes  :)