6. Petya saw a bank advertisement: "Deposit 'Super-Income' - up to $10 \%$ annually!". He became interested in this offer and found it on the bank's website. The conditions turned out to be slightly different, as reflected in the table.

| Interest period | from 1 to 3 months | from 4 to 6 months | from 7 to 9 months | from 10 to 12 months |
| :---: | :---: | :---: | :---: | :---: |
| Rate | $10 \%$ | $8 \%$ | $8 \%$ | $8 \%$ |

*     - interest is credited at the end of the period.

What is the actual effective annual interest rate of this deposit? Round your answer to the tenths.
Answer: 8.8%.

The effective interest rate implies the capitalization of interest, that is, adding it to the deposit amount. Let's say Petya deposited X rubles into the described deposit, then by the end of the year, he will have

$X *(1+0.1 / 4) *(1+0.08 / 4) *(1+0.08 / 4) *(1+0.08 / 4) \approx X * 1.0877$.

That is, the effective interest rate is approximately $8.8 \%$.