Compound Interest D9F75B
1. **Problem statement:** Curtis wants to buy a trumpet costing 360. He deposits 285 into a savings account with 1% monthly compound interest. We need to find the smallest whole number of months $n$ so that the amount in the account is at least 360.
2. **Formula:** The compound interest formula is:
$$ A = P(1 + r)^n $$
where:
- $A$ is the amount after $n$ months,
- $P = 285$ is the principal,
- $r = 0.01$ is the monthly interest rate,
- $n$ is the number of months.
3. **Goal:** Find the smallest integer $n$ such that:
$$ 285(1.01)^n \geq 360 $$
4. **Trial and improvement:** We test values of $n$:
- For $n=25$: $$ 285 \times 1.01^{25} = 285 \times 1.2824 = 365.88 \geq 360 $$ (enough money)
- For $n=24$: $$ 285 \times 1.01^{24} = 285 \times 1.2697 = 361.97 \geq 360 $$ (enough money)
- For $n=23$: $$ 285 \times 1.01^{23} = 285 \times 1.2571 = 358.39 < 360 $$ (not enough)
5. **Conclusion:** The smallest whole number of months is $\boxed{24}$ months.
Curtis must wait 24 months to have enough money to buy the trumpet.