Math problem

Question

A textbook store sold a combined total of 369 chemistry and psychology textbooks in a week. The number of psychology textbooks sold was 43 less than the number of chemistry textbooks sold. How many textbooks of each type were sold?

Answer 1

Hello Elmer,

Okay, so let's use the following variables to represent the books in your problem, okay? 

c = chemistry books
p = psychology books 

The problem is clear: A total of 369 textbooks were sold, right? You just need to determine how many of each kind were sold given the information provided. 

Therefore: 

369 = p + c 

We also know the number of psychology textbooks sold was 43 LESS than the number of chemistry books sold, right? 

Therefore: 

p = c - 43 


Now, you know what p is equal to, but this does not quite resolve the problem is, does it? Therefore, we need to complete our work. 

Remember: c + p = 369

Now, c + c - 43 = 369  PLEASE NOTE: I have plugged the expression of c - 43 for the value of p (psychology texts) due to the equation we just worked. 


Therefore, 2c = 412

c = 206 
p = 163 


Add these two together and you will see that the total is 369 total textbooks. 

Please let me know if this answers your question or if you need further explanation. I hope you have a great Sunday. 

~Mark B.