Suppose that $20,000 is invested at continuous rate r and grows to$81,104 in 28 years. Find the interest rate r.

Find the time required for a $1000 investment to (a) double at interest rate r, compounded continuously, and (b) triple at interest rate r, compounded continuously. Round your results to two decimal places.$r = 2.5%$

Use the compound interest formula, $A(t)=P\left(1+\frac{r}{n}\right)^{n t}$.

Use properties of rational exponents to solve the compound interest formula for the interest rate, $r$.

Solve for the unknown interest rate in each of the following:

A sum of $1000 was invested for 4 years, and the interest was compounded semiannually. If this sum amounted to$1435.77 in the given time, what was the interest rate?

Bill Rich signed a 180-day note for $1,250. He repaid the loan when due with interest at an annual rate of 12 % using a banker's year.

Tony Colito paid$19.50 in interest on a loan of $2,600 for 1 month. What rate of interest did he pay?

A $4000 certificate of deposit is purchased for$4000 and is held for eleven years. If the certificate earns an effective rate of 7%, what is it worth at the end of that period?

Find the simple interest paid to the nearest cent for each loan amount, interest rate, and time. $1,000, 7%, 2 years

Find the compound amount and compound interest if $4000 is invested for six years and interest is compounded continuously at the given annual rate. 9%

Suppose that $10,000 is invested at continuous rate r and grows to$17,160 in 9 years. Find the interest rate r.

For the following exercise,

Determine the value of the annuity for the indicated monthly deposit amount, the number of deposits, and the interest rate.

Deposit amount: $\$ 100$; total deposits: $120$ ; interest rate: $10 \%$, compounded semi-annually

Find the time required for a $1000 investment to (a) double at interest rate r, compounded continuously, and (b) triple at interest rate r, compounded continuously. Round your results to two decimal places.$r = 7 %$

The formula

$$I_t=\frac{I_f}{1-T}$$

gives the taxable interest rate $I_t$ equivalent to the tax-free interest rate $I_f$ for a person in the $(100 \cdot T) \%$ tax bracket. Solve for $T$.

Bill Rich signed a 180-day note for $1,250. He repaid the loan when due with interest at an annual rate of 12 % using a banker's year.

Kelly Bullock borrowed$4,800 for 6 months and paid $264 interest. What rate of interest did she pay?