According to the equation

[Problem solving process]

Set the value x, and then

6*x*0.4%=7.8

2.4x=780

x=325

2. How much money was saved a year ago is the principal. 4.5 yuan is an interest tax, that is, interest ×20%= principal × interest rate× number of periods ×20%, in which the number of periods = 1 year, and the annual interest rate =2.25%. So this problem can be solved by using the relationship among principal, interest, interest rate, number of installments and interest tax.

It's good. It shows that you have a clear understanding of these savings terms and their relationships. Let's answer this question together.

Solution: Suppose this depositor deposited X yuan in the bank a year ago. According to the meaning of the question, the equation x×2.25%× 1×20%=4.5 is listed.

Solution, x= 1000

So the depositor deposited 1000 yuan in the bank.

Let's look at another example.

The annual interest rate of one-year time deposit is 2.25%, and the interest earned is subject to 20% interest tax. For example, if you deposit 100 yuan a year, the formula for calculating the after-tax interest of the due depositors is: after-tax interest =100× 2.25%-100× 20% =

Analysis: According to the meaning of the question, the principal × annual interest rate × (1-20%) = 450 yuan. Using this equivalence relation, we can set an unknown number and make a linear equation.

Solution: Assuming that the deposit principal is X yuan, according to the meaning of the question, you can get

2.25%( 1-20%)x=450

Solve this equation and get x=25000.

So the depositor deposited a principal of 25,000 yuan.

3.