Atextbook store sold a combined total of 266 math and biology textbooks in a week. the number of math textbooks sold was 54 more than the number of biology textbooks sold. how many textbooks of each type were sold?

Let m and b represent the numbers of math and biology books sold, respectively. The problem statement tells you ...

... m + b = 266

... m - b = 54 . . . . . . . 54 more math books were sold

Adding these two equations gives you ...

... 2m = 320

... m = 160 . . . . . divide by 2

... b = 160 -54 = 106 . . . . 54 fewer biology books were sold.

160 math textbooks and 106 biology textbooks were sold in a week.

yes. we do proportions in probabilities.