Interest is Interesting

Instructions

In this exercise you'll be working with savings accounts. Each year, the balance of your savings account is updated based on its interest rate. The interest rate your bank gives you depends on the amount of money in your account (its balance):

• 3.213% for a negative balance (results in negative interest).
• 0.5% for a positive balance less than 1000 dollars.
• 1.621% for a positive balance greater or equal than 1000 dollars and less than 5000 dollars.
• 2.475% for a positive balance greater or equal than 5000 dollars.

Each year the government allows you to donate a percentage of your money to charity, tax free. Because you're a nice person, if your balance ends up positive at the end of the year, you take the tax-free percentage and double it, rounding down to the nearest whole dollar. You don't mind paying tax on the second half of the donation.

You have three tasks, each of which will deal with your balance and its interest rate.

1. Calculate the interest rate

Implement the interestRate function to calculate the interest rate based on the specified balance:

interestRate 200.75m
// => 0.5f

Note that the value returned is a single.

2. Calculate the interest

Implement the interest method to calculate the interest based on the specified balance:

interest 200.75m
// => 1.00375m

Note that the value returned is a decimal.

3. Calculate the annual balance update

Implement the annualBalanceUpdate function to calculate the annual balance update, taking into account the interest rate:

annualBalanceUpdate 200.75m
// => 201.75375m

Note that the value returned is a decimal.

4. Calculate how much money to donate

Implement the amountToDonate function to calculate how much money to donate to charities based on the balance and the tax-free percentage that the government allows:

let balance = 550.5m
let taxFreePercentage = 2.5
amountToDonate balance taxFreePercentage
// => 27

Note that the value returned is an int.