Answer:
d. 126; 70
Step-by-step explanation:
given that Ron  finds 9 books at a bookstore that he would like to buy, but he can afford only 5 of them.
Out of 9 books he has to select 5 of them
Here selection of books can be done in any order.  Hence order does not matter
No of ways he selects 5 books out of 9 books = 9C5 
= 126
Part II
One book is a must
Hence he has options only 4 books from the remaining 8.
No of ways when one book is compulsory = selecting 3 books from 8 books
= 8C4
= 70
Option d is right.
 
        
             
        
        
        
Answer:

Step-by-step explanation:
This is <em>a separable differential equation</em>. Rearranging terms in the equation gives
                                                 
Integration on both sides gives
                                             
where  is a constant of integration.
 is a constant of integration.
The steps for solving the integral on the right hand side are presented below. 
                                
Therefore,
                                         
Multiply both sides by 
                                
By taking exponents, we obtain
       
Isolate  .
.
                  
Since  when
  when  , we obtain an initial condition
, we obtain an initial condition  .
. 
We can use it to find the numeric value of the constant  .
.
Substituting  for
 for  and
 and  in the equation gives
 in the equation gives
                          
Therefore, the solution of the given differential equation is
                                    