To solve this problem, we can use the formula for compound interest:
A = P(1 + r/n)^(nt)
where:
A = final amount
P = principal (initial amount)
r = annual interest rate (as a decimal)
n = number of times the interest is compounded per year
t = time (in years)
In this case:
P = $11,000
r = 2.5% = 0.025 (since it's compounded monthly, we need to divide by 12 to get the monthly rate)
n = 12 (compounded monthly)
t = 21 years
Plugging in these values, we get:
A = 11000(1 + 0.025/12)^(12*21)
A ≈ $16,180.64
Therefore, the value of the account at the child's twenty-first birthday will be approximately $16,181.