Question

Zu welchem Zinsfuss bringen 720 Fr. in 330 Tagen ebensoviel Zins wie 675Fr.in 8 Monaten zu 5.5%

Answer 1

8 months * 30 days/month = 240 days
5.5 % = .05/year = 1.37 * 10^-4 /day
assuming simple interest
720 * x * 330 = 675 * 1.37*10^-4 * 240
x = 9.34 * 10*-5 /day
365 x = .0341
* 100 = 3.41 %

Answer 2

I interpret your question as asking "At what interest rate (Zinsfuss) will 720 Francs in 330 days yield as much interest (Zins) as 675 Francs for 8 Monate at 5.5%? "

The latter amount is (8/12 yr)*(0.055)(675) = $24.75

You require 720*(Interest rate)*(11/12) = 24.75

The answer I get is Zinsfuss = 3.75%

Answer 3

I used 5% instead of 5.5 %. Use drwls' numbers.