Math question please help best answer 10 points

a school librarian bought 56 books, some at $3.50 each and others at $4.50 each. if the total cost of these books was $240, how many books that cost $3.50 each were bought?

let x= number of books that cost $3.50
y=number of books that cost $4.50

make some equations:
x+y=56 <-----equation 1
3.5x+4.5y=240 <----equation 2

from eq 1:
y=56 - x

substitute this to equation 2
3.5x +4.5(56-x)=240
3.5x + 252 - 4.5x=240
x = 12
x= 12
therefore there are 12 books that cost $3.50. :))

You have two unknowns: Number of $3.50 books, x, and number of $4.50 books, y, so you need two equations. These can be found in your sentences.

"a school librarian bought 56 book" gives the equation x + y = 56

"some at $3.50 each and others at $4.50 each. if the total cost of these books was $240" gives the equation $3.50x + $4.50y = $240

Solve the first equation for y, then put it in the second equation in place of y

x + y = 56

y = 56 - x

*******
3.5x + 4.5y = 240

3.5x + 4.5(56 - x) = 240

3.5x + 252 - 4.5x = 240

3.5x - 4.5x = 240 - 252

-x = -12

x = 12

There are 12 books that are $3.50

x= # books at 3.50
y+ # books at 4.50

x+y=56 and
3.5x + 4.5y = 240
solve first equation for x==> x=56-y now substitute into second equation

3.5(56-y) + 4.5y =240
196-3.5y+4.5y = 240
y=44 and x = 12 check by putting values back into second equation
3.5*12 + 4.5*44 ==>42+198 ==> it = 240 so answer checks

Let cost of x books for @ 3.50
so (56 – x) books for @ 4.50
3.5x + 4.5(56 – x) = 240
3.5x + 252 – 4.5x = 240
x = 12 book @ 3.50
and (56 – 12) = 44 books @ 4.5
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Why don't you do your own homework?