提米（Timmy）想将一笔钱投资到以下投资计划之一。

计划	描述
计划 A	每年支付 2% 的单利
计划 B	每年支付 2% 的复利

哪种投资计划对提米来说是更好的选择？解释你的答案。 答案 : ... ... 玛丽（Mary）将 $8000 存入一个储蓄账户，年单利率为 3.5%。计算她 12 年年底的储蓄总值。 答案 $ ... 彼得（Peter）在 2010 年至 2024 年期间投资了一项投资计划，金额为 $50 000。
他的投资价值在每年年底增长 $r\%$。
在 2024 年底，彼得投资的总价值为 $65 320。 计算 $r$ 的值。 答案 $r$ = ... (d) 新加坡元 (SGD) 与泰铢 (THB) 之间的当前汇率为 SGD 1 = THB 27.16。 苏珊（Susan）在泰国购物时买了一个包。该包的原价为 THB 56 000，苏珊以 15% 的折扣购买了它。 苏珊使用信用卡支付了包的费用，该信用卡向她额外收取了 2% 的境外交易费。 计算苏珊必须支付的总金额（包括信用卡费），以新加坡元 (SGD) 表示。将你的答案保留到最接近的分。 答案 $ ...

1. Choose the better investment plan and justify using the meaning of compound interest

Both plans have the same annual rate of $2\%$. Plan B is better because compound interest is calculated on the accumulated amount each year, while simple interest is calculated only on the original sum.

1. Calculate the simple interest earned over 12 years

Simple interest
$= 8000 \times \frac{3.5}{100} \times 12$
$= 3360$

2. Add the interest to the original deposit to find the total value

Total value
$= 8000 + 3360$
$= 11360$

1. Set up the compound growth equation for 14 yearly increases

From 2010 to 2024, there are $2024-2010=14$ yearly increases.

Let the yearly multiplier be $1+\dfrac{r}{100}$.

$50000\left(1+\frac{r}{100}\right)^{14}=65320$

2. Isolate the yearly growth multiplier

$\left(1+\frac{r}{100}\right)^{14}=\frac{65320}{50000}$

$1+\frac{r}{100}=\left(\frac{65320}{50000}\right)^{\frac{1}{14}}$

3. Calculate the percentage rate $r$

$\frac{r}{100}=\left(\frac{65320}{50000}\right)^{\frac{1}{14}}-1$

$r=100\left[\left(\frac{65320}{50000}\right)^{\frac{1}{14}}-1\right]$

$r\approx 1.920$

1. Find the discounted price of the bag in THB

A 15% discount means Susan pays $100\%-15\%=85\%$ of the original price.

$56000\times 0.85=47600$

Discounted price $=\text{THB }47600$

2. Include the 2% overseas transaction fee

A 2% fee means Susan pays $100\%+2\%=102\%$ of the discounted price.

$47600\times 1.02=48552$

Total charged $=\text{THB }48552$

3. Convert the total amount from THB to SGD and round to the nearest cent

Since SGD 1 = THB 27.16,

$\text{Amount in SGD}=48552\div 27.16=1788.953\ldots$

Correct to the nearest cent, this is $\char36{}1788.95$.