Question

Three pens and a book cost 1,200 and 2 pens and a book also cost 1,000.Find the cost of 15 pens and 12 books.

Answer 1

Let the cost of pens be x and books be y
Then we get 3x+y=1200 and 2x+y=1000
Here we can substitute y=1000-2x
So putting the value of y in the first eq we get
3x + 1000 - 2x=1200
x=200
So putting the value of x we get
2(200)+y=1000
y=600
So cost of one pen= 200 and cost of one book = 600.
Therefore cost of 15 pens = 15 * 200 =3000
And cost of 12 books = 12 * 600 = 7200