Question

A textbook store sold a combined total of 475 sociology and history textbooks in a week. The number of history textbooks sold was 83 less than the number of sociology textbooks sold. How many textbooks of each type were sold?

Answer 1

Let the number of Sociology books =  y; the number of History books = x

⇒  x + y = 475   (2)
also since the number of history books sold was 83 less than sociology, 
then x = y - 83  (1)   

BY substituting (1) into (2)
⇒  (y - 83) + y = 475
                  2y = 475 + 83
                    y = (558 ÷ 2)
                    y = 279

⇒ x  =  279 - 83
     x  =  196

∴ Number of History books is 196 & number of Sociology books is 279.