If the price was "4 for $10", that would be $2.50 for one, and you should
have paid $12.50 for 5 of them.  However, you said the price was "$5 each or
4 for $10 ."  This looks like some sort of sale, but the sale price applies
only under some circumstances.

This may be similar to a "two for the price of one" sale.  In such a case, I
would not expect the offer to imply "one for half price" -- I would need to
buy two to get  the sale price.

So, an offer to sell some things at the price of "$5 each or 4 for $10" is
open to interpretation.  Some possibilities:

Buy one to three items, pay $5 each; buy 4 or more items, pay $2.50 each.
(Your interpretation?)

Buy one to three items, pay $5 each; buy 4 items pay $2.50 each, but the
seller is not offering to sell more than four per customer.  (In other
words, quantities are limited).

Buy items in multiples of 4 and pay $2.50 each, but $5 each for each "odd"
(that is, each item remaining after the quantity purchased is divided by 4).
(The clerk's interpretation?)  This interpretation might be more common for
items naturally purchased in twos and fours, such as tires.

How about "pay $5 each for one to three items, $10 for four items; for each
item over 4, pay another $5 each."  This might be the case when the 4 for
$10 is tied to conditions, such as having a coupon.  To get 8 for $20, I
would need two coupons; with one coupon I would need to pay $30 for 8.
(Assuming I was allowed to use two coupons for one purchase.)


Systems analysts should be aware that things aren't always interpreted as
meant.  We need to ask questions, use examples, check our understanding.
As you say, maybe we are guilty from time to time.



>heh Gosh, we could relate experiences all day. Maybe even we are guilty
from
>time to time ;-) OK, one incident that seems to stand out with me -I  was
>buying something - let's say, $5 each or 4 for $10. I bought 5 of the
>items - clerk charges me $15. "You bought 4 for $10 and an extra one". I
>couldn't get though...