2。 450/( 1-20%)=562.5 The pre-tax interest rate is 562.5 and the annual interest rate is 2.25%, so the principal is 562.5/2.25% = 25,000.

3。 The after-tax interest is 8 14.05-800= 14.05, and the pre-tax interest is14.05/(1-20%) =17.5625.

Interest rate:17.5625/800 = 2.195%.

4。 (536-500)/500= 7.2%

5。 2000*( 1+8.64%)=2 172.8

6。 (3243-3000)/3= 8 1, that is, the annual interest is 8 1 yuan. 8 1/3000=2.7%

7。 The pre-tax interest is 48.6/(1-20%) = 60.75/2 = 30.375, and the deposited money is 30.375/2.43%= 1250.