[RESOLVED] Calculate fees

[Orbit__]

For example Paypal has a fees of 2.5%+.25

If someone send me 5$ i'll recieve
5-((5*2.5/100)+0.25) = 4.625

but how do i convert the recieved money 4.625 back to 5

i tried 4.625*102.5/100 +.25=4.99 but i want an exact value

how can that be possible?

[MaximilianMayrhofer]

Well you could start with the fact that your math is wrong.

let val received = x and original val = y:

x = y - 0.025y - 0.25

x = 0.975y - 0.25

x + 0.25 = 0.975y

y = (x + 0.25) / 0.975 --> which is not the same as x * 102.5 / 100 + 0.25

Plug x = 4.625 into that and you'll get exactly 5.

[krtxmrtz]

For example Paypal has a fees of 2.5%+.25

If someone send me 5$ i'll recieve
5-((5*2.5/100)+0.25) = 4.625

but how do i convert the recieved money 4.625 back to 5

i tried 4.625*102.5/100 +.25=4.99 but i want an exact value

how can that be possible?

If you call F the final amount you get (4.625) and A the initial 5$ they send you, you have:

F = A - (2.5 A / 100 + 0.25) = A - (0.025 A + 0.25)

So now you invert the equation:

F = A - 0.025 A - 0.25 = (1 - 0.025)A - 0.25 = 0.975A - 0.25
and
A = (F + 0.25) / 0.975 = (4.625 + 0.25) / 0.975 = 4.875 / 0.975 = 5