You deposited 6,000 in a savings account, and after 4 years, your account balance is 7,800. What was the annual interest rate on the account?

To solve this problem, we can use the formula for compound interest, which is A = P(1 + r/n)^(nt), where:

• A is the amount of money accumulated after n years, including interest.
• P is the principal amount (the initial amount of money).
• r is the annual interest rate (in decimal).
• n is the number of times that interest is compounded per year.
• t is the time the money is invested for in years.

In this case, we know that:

• A = 7,800
• P = 6,000
• n = 1 (since interest is compounded annually)
• t = 4 years

We want to find r. So, we can rearrange the formula to solve for r:

r = ((A/P)^(1/(nt)) - 1) * n

Substituting the known values:

r = ((7800/6000)^(1/(1*4)) - 1) * 1

r = (1.3^0.25 - 1) * 1

r ≈ 0.067 or 6.7%

So, the annual interest rate on the account was approximately 6.7%.