Question #ac2d1

Question

1434 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2017-06-16T12:47:19

I got $15$ pens at $$6$ each.

Call the number of pens $x$ and the cost of one pen $y$ we get:

At the original price:
$xy=90$

If we subtract $$1$ from the original price we can buy $3$ more pens or:
$(x+3)(y-1)=90$

so
$(x+3)(90/x-1)=90$
$90-x+270/x-3=90$
$-x^2+270-3x=0$

Using the quadratic Formula we get that:

$x_1=15$ (we get a negative solution as well $x_2=-18$ ).

So the total number of pens is $15$ and the cost of one pen will be:
$y=90/x=90/15=$6$