Andrew M. answered • 09/04/16
Tutor
New to Wyzant
Mathematics - Algebra a Specialty / F.I.T. Grad - B.S. w/Honors
Let x = # books bought at 18
Let y = # books bought at 12
1) x + y = 120 total number of books bought
2) 18x + 12y = 1920 total amount of money spent
in equation 1 solve for x in terms of y
x+y = 120
x = 120-y
Replace x in equation 2 with 120-y and solve for y
to find out how many books were bought at 12 pounds
18(120-y) + 12y = 1920 multiply through the parenthesis
2160 - 18y + 12y = 1920 combine the y terms
2160 - 6y = 1920 subtract 2160 from both sides
-6y = 1920-2160
-6y = -240 divide both sides by -6
y = -240/(-6)
y = 40
x = 120-y = 120-40 = 80
He bought 80 books at 18 pounds and 40 books at 12 pounds
Check: 80(18)+40(12) = 1920
1440+480 = 1920
1920 = 1920
Equation balances and answer is correct
Andrew M.
Yes. A system of equations, solved by substitution.
You could also solve by elimination by multiplying the
first equation by -18 or -12 and then adding to
eliminate one variable and solve for the other.
Hope this helped. :-)
Report
09/05/16
William Z.
09/04/16