Kate borrowed $400 from her friend. She will repay this amount plus 3 percent simple interest after one year. What is the total amount she will pay her friend?

The answer is $412.

Let's first calculate simple interest. Simple interest (I) can be expressed as:

I = P * r * t

P - principal

r - rate

t - time period

It is given:

I = ?

P = $400

r = 3% = 0.03

t = 1 year

Therefore:

I = P * r * t = 400 * 0.03 * 1 = 12

The total amount Kate will repay is the principal amount (P) plus 3% simple interest (I):

P + I = 400 + 12 = $412