How many textbooks of each type were sold?

Question

A textbook store sold a combined total of475 biology and psychology textbooks in a week. The number of biology textbooks sold was67 more than the number of psychology textbooks sold. How many textbooks of each type were sold?

Answer 1

Hi,

The key to word(story) problems is to translate the words into concise, precise math expressions (with variables and operations).  Once you’ve done that, the math is easy.

Let’s assign variables:
        Let B = number of biology textbooks sold
              P = number of psychology textbooks sold

O.K., translate:
    “textbook store sold a combined total of475 biology and psychology textbooks”
                       Means      B + P = 475
    “number of biology textbooks sold was 67 more than the number of psychology textbooks sold”   

                        means     B = 67 + P
    “How many textbooks of each type were sold?”  means     report B, P

Now, the math:
     Use the second equation to substitute for each B in the first equation.
                                     B + P = 475
                            (67 + P) + P = 475
                                     2P = 408
                                      P = 204

      Put that value of P into either equation to solve for B:
                               B + P  = 475
                               B + 204 = 475
                                  B = 271

Report B=271, P=204

Checking:
      Is   271 + 204 = 475   ?     Yes
      Is    271 = 67 + 204    ?    Yes