For a fixed principal, the ratio of the amounts for 3 and 2 years is 21:20. What is the rate of interest? (Enter the numerical value only, not the % sign.)

Let's assume the principal amount is P.

According to the given information, the ratio of the amounts for 3 and 2 years is 21:20.

Let's calculate the amount after 3 years: Amount after 3 years = P + (P * r * 3), where r is the rate of interest.

Let's calculate the amount after 2 years: Amount after 2 years = P + (P * r * 2)

According to the given ratio, we have the equation: (P + (P * r * 3)) / (P + (P * r * 2)) = 21/20

To solve this equation, we can cross-multiply: 20 * (P + (P * r * 3)) = 21 * (P + (P * r * 2))

Expanding the equation: 20P + 20P * r * 3 = 21P + 21P * r * 2

Simplifying the equation: 60P * r = 42P * r

Dividing both sides by P * r: 60 = 42

This equation is not possible, as 60 cannot be equal to 42.

Therefore, there is no valid rate of interest that satisfies the given conditions.