Riddle for the day - Tough one I think - Do you know?

if he paid $.80 (80 cents) per hundred, each unit would cost $.008 (or 0.8 cent). taking away 4 cents would reduce the quantity by 5.

my guess is that he ordered 100 favors for $0.80. if he only had $0.80 to spend and the price was $0.04 higher per hundred, then he would only be able to buy 95 units with his $0.80.

is this right??

If I understand the problem correctly, there is more than one solution.

This is almost what thorman had:
105 @ $0.80 per 100 = $0.84
100 @ $0.84 per 100 = $0.84

But there is also:
55 @ $0.40 per 100 = $0.22
50 @ $0.44 per 100 = $0.22

or:
205 @ $1.60 per 100 = $3.28
200 @ $1.64 per 100 = $3.28

and so on.

the complete solution is this:

no. of favors = x
price in cents per 100 = y

he paid x times y/100 = xy/100
different prices would have been x-5 times (y+4)/100 = (x-5) (y+4) / 100

These are the same, so

xy/100 = (x-5) (y+4)/100
xy = (x-5)(y+4)
xy = xy +4x -5y -20
5y = 4x -20
y = 0.8x -4
In all answers x must be an integer, x and y must be > 0 (x>5 to keep y>0)

Answer
The official answer is .96. I do not know why but that is the answer.