Question

a textbook store sold a combined total of 220 biology and psychology textbooks in a week. the number of psychology textbooks sold was 40 less than the number of biology textbooks sold. how many textbooks of each type were sold?
your answer
number of biology textbooks sold:
number of psychology textbooks sold:

Explanation:

Step1: Define variables

Let \( x \) be the number of biology textbooks sold. Then the number of psychology textbooks sold is \( x - 40 \).

Step2: Set up equation

The total number of textbooks sold is the sum of biology and psychology textbooks, so \( x+(x - 40)=220 \).

Step3: Solve the equation

Simplify the left - hand side: \( 2x-40 = 220 \).
Add 40 to both sides: \( 2x=220 + 40=260 \).
Divide both sides by 2: \( x=\frac{260}{2}=130 \).

Step4: Find the number of psychology textbooks

The number of psychology textbooks sold is \( x - 40=130 - 40 = 90 \).

Answer:

Number of biology textbooks sold: \( 130 \)
Number of psychology textbooks sold: \( 90 \)