I have some problems understanding a question in a math class test for 10 year olds.
The question is:
Someone pays in 200€ to a bank. The interest rate is 3.75%. Some time later, he looks at the account balance and he sees that there are 235€ now. How much time passed?
I would calculate this using logarithms, but the interesting part here is that they don't even know square roots, not to mention logarithms.
Is there any easy way to calculate this without logarithms that I overlooked?