Question

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

Answer 1

@jim_thompson5910

Answer 2

@texaschic101

Answer 3

`A textbook store sold a combined total of
434 psychology and biology textbooks in a week.`

let
x = # of psychology books
y = # of biology books

what equation can we form from the information given above?

Answer 4

x+y=434?

Answer 5

yep

Answer 6

`The number of biology textbooks sold was 86 less than the number of psychology textbooks sold.`

what equation can we form here?

Answer 7

x+y-86=434?

Answer 8

`The number of biology textbooks sold was 86 less than the number of psychology textbooks sold`

x = # of psychology books
y = # of biology books

(number of bio books) = (number of psych books) - 86
(y) = (x) - 86
y = x - 86

so we can form the equation y = x-86

agreed?

Answer 9

yes

Answer 10

the system of equations is then

x+y = 434
y = x-86

Answer 11

\[\Large \color{red}{y} =\color{red}{x-86}\]
------------------------
\[\Large x+y = 434\]
\[\Large x+\color{red}{y} = 434\]
\[\Large x+\color{red}{x-86} = 434\]
\[\Large 2x-86 = 434\]
\[\Large x = ???\]

Answer 12

x=260

Answer 13

thank you @jim_thompson5910