A textbook store sold a combined total of

Question

A textbook store sold a combined total of 393

psychology and biology textbooks in a week. The number of biology textbooks sold was 79

less than the number of psychology textbooks sold. How many textbooks of each type were sold?

Answer 1

Let us assume p is the number of psychology books and b is the number of biology textbooks.

 

set up first equation: 

 

we know that the total number of books sold was 393

p+b=393 

 

set up second equation: 

 

we know that there were 79 less biology book sold that psychology so...

p = b + 79

 

subsitute p in the first equation to solve for b

 

solve value for p

 

Answer 2

If P represents the number of psychology books sold and B the number of biology:

 

P + B = 393 (from 1st sentence)

B = P - 79 (from 2nd sentence)

P + P - 79 = 393 (from replacing B in terms of P)

2P = 472 (from combining terms and adding 79 to both sides)

P = 236 (from diving both sides by 2)

B = 236 - 79 = 157