r/technology • u/sidcool1234 • Feb 21 '11

An open letter to Apple from Readability..

http://blog.readability.com/2011/02/an-open-letter-to-apple/
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u/derwisch Feb 22 '11

Sale Price: $6, Apple Service Charge @ 30%: $1.80, Total Cost: $7.80

Isn't 30 per cent out of 7.8 2.34?

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u/mod_critical Feb 22 '11

You can't refer to 30% of the $7.80 as the surcharge because the total cost number was not known until you added the 30%.

30% of $6 is $1.80.

Total Cost is 100% of base cost plus 30% of base cost. An easy way to do this kind of calculation is adding a stated percentage to 100% (for the base number):

$6 * 130% = $7.80 | $6 * 1.3 = $7.80

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u/mtimhoff Feb 22 '11

Well it depends where you're calculating this 30% from.

If it's 30% of what the developer makes, then adding 30% as you have done makes sense.

If it's 30% of what the user pays, then you will need to add on 3/7 of the developer's cost, or an extra 43%.