Question

A textbook store sold a combined total of 423 biology and physics textbooks in a week. The number of physics textbooks sold was 81 less than the number of biology textbooks sold. How many textbooks of each type were sold?

Answer 1

The number of Biology textbooks sold is 252 and the number of Physics textbooks sold is 171.

Step-by-step explanation:

Let's call
`x` to the number of biology textbooks.

The question tells us that the number of physics textbooks sold was 81 less than the number of biology textbooks sold, so we would write this as
`x-81`.

On the other hand, we know that the sum of both type of textbooks sold is 423, so we would have:

biology textbooks + physics textbooks = 423.

We will substitute this last expression using our variable x and solve for x:

`x+ (x-81)=423\\x+x-81=423\\2x-81=423\\2x=423+81\\2x=504\\x=504/2\\x=252`

Thus, the number of biology textbooks sold is 252.

The number of physics textbooks sold would be 252-81 = 171.