15 years, deposited in 450 yuan every six months. The interest rate for the first seven and a half years is 10%, and the interest rate for the last seven and a half years is 1 1%.

Is that what the title means?

Because the interest is calculated every six months, the interest for half a year is 5% and 5.5%. Don't make mistakes.

Deposit for the first seven and a half years: 450 * (1.05 15-1)/0.05 = 9710.35, and deposit for15 for half a year, with annual interest rate1.05.

Deposits in the last seven and a half years: 450 * (1.05515-1)/0.055 =10083.90.

The two eventually add up: 21678.13+10083.90 = 31762.03.

Accrued interest = 31762.03-450 * 30 =18262.03