Question 998400
 a student bought some packets of pen for 2000 dollar.
 if she had paid 24 dollar less for each packet she could have bought 3 more packets.
 how many packet of pen did she buy?
:
Let x = no. of packets bought
then
{{{2000/x}}} = cost of each packet
:
{{{2000/x}}} - 24 = {{{2000/((x+3))}}}
multiply equation by x(x+3), cancel the denominators and you have
2000(x+3) - 24x(x+3) = 2000x
2000x + 6000 - 24x^2 - 72x = 2000x
subtract 2000x from both sides
6000 - 24x^2 - 72x = 0
A quadratic equation
-24x^2 - 72x + 6000 = 0
simplify, divide by -24
x^2 + 3x - 250 = 0
you would expect an integer solution to a problem like this but I got
x = 14.4 packets
:
And this checks out
2000/14.4 = 138.90 for each packet
When you drop the cost by $24, you have 114.90
2000/114.90 = 17.4 packet which is 3 more than original