Wishbone: Uhm, GOG? You forgot how to math?
The discount percentages you advertise do not match the prices you charge. Admittedly, the difference is small, but this is
very basic math we're talking about. How on earth can you miscalculate a 50% discount?
Exploring this mathematically...
10.09 / 19.99 = 0.50475237618809404702351175587794
5.09 / 19.99 = 0.25462731365682841420710355177589
Subtracting each of these from 1.0 in order to get the discount percentage gives:
1.0 - 0.50475237618809404702351175587794 = 0.49524762381190595297648824412206
1.0 - 0.25462731365682841420710355177589 = 0.74537268634317158579289644822411
Rounding each of those off to two decimal places equals: 0.50 or 50%, and 0.75 or 75%, so as decimal fractions to two places or as integer percentages, the values 50% and 75% are at least mathematically accurate. What makes these numbers seem strange however is that it appears as if the sale prices were arrived at in dollar amounts by some other means and the percentage discounts computed from that, rather than what you might expect such as taking a discount percentage and applying it to the base price which is most likely how things are normally done. If that happened, then they would take 19.99 and subtract 50% and 75% from it respectively to arrive at the prices $10.00 ($9.995) and $5.00 ($4.9975), leaving one wondering where that extra 9 cents comes from.
It does leave one wondering how the prices are calculated however as it seems it isn't from taking the price in the local currency and applying a percentage discount to it, but rather taking a discounted price and calculating what the discount amounts to as an integer percentage. In short, it looks odd but is still mathematically correct. :)
The other possibility, is that the way they're calculating things might involve currency conversions and perhaps applies premature rounding too early, causing an error margin that compounds on subsequent calculations that result in an error that is visible above the rounding accuracy.
These last two paragraphs are just a bit of educated speculation on my part though, GOG would have to come forward and disclose their algorithms with us to be sure, but I have to admit - while the percentages shown are mathematically accurate to the degree of expected rounding, they are odd to see and may raise some eyebrows. :)
Update: One further possibility I thought of after posting, was that they might calculate the discount, then round it
up to the next .?9 value for marketing purposes. If so that's kind of ugly. If they were going to do that, IMHO a better more balanced way to do it would be using regular rounding mechanics but rounding to the final digit 9 instead of the final digit 0, in which case prices pre-rounded that end with 0.39 or lower would round down to .?9 and .40 and above would round up to the next 0.?9. Clearly though, 50% of $19.99 is $9.995, which if rounded normally to two decimal places would be $10.00, or if rounded to a final digit of 9 as I propose, would cause it to round downward to $9.99 instead of upward to $10.09. So if they are doing rounding to 9s, then they're mathematically doing rounding up rather than rounding off.
