Improve Concept Exercise: Freelancer Rates (#1472)

concepts/numbers/.meta/config.json

@@ -1,5 +1,5 @@
 {
   "blurb": "There are two different kinds of numbers in JavaScript - numbers and bigints. Numbers are for everyday use and are always floating point numbers.",
   "authors": ["SleeplessByte"],
-  "contributors": []
+  "contributors": ["junedev", "JaPatGitHub"]
 }

concepts/numbers/about.md

@@ -28,6 +28,14 @@ There are two built-in objects that are useful when dealing with numbers:
 - [`Number`][built-in-number]: static properties for common / useful values, static methods for [type-checking][concept-type-checking] and [type-conversion][concept-type-conversion], instance methods for [type-conversion][concept-type-conversion] and [formatting numbers as strings][string-formatting].
 - [`Math`][built-in-math]: properties and methods for mathematical constants and functions, does **not** work with `BigInt`.
 
+`Math` also includes methods for rounding numbers.
+You can read more about the available rounding options in this [javascript.info article on rounding][ref-math-object-rounding].
+
+```javascript
+Math.floor(234.34); // => 234
+Math.ceil(234.34); // => 235
+```
+
 The `Number` built-in global `object` is _also_ a global `function` that can be used to convert _almost anything_ number-like to a `number`.
 It is less forgiving than _parsing_ a `string` to a `number`.
 
@@ -86,6 +94,7 @@ See [0.30000000000000004.com](https://0.30000000000000004.com/) for a brief expl
 [comparison]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
 [lexical-grammar]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#numeric_literals
 [string-formatting]: /tracks/javascript/concepts/string-formatting
+[ref-math-object-rounding]: https://javascript.info/number#rounding
 [concept-comparison]: /tracks/javascript/concepts/comparison
 [concept-type-checking]: /tracks/javascript/concepts/type-checking
 [concept-type-conversion]: /tracks/javascript/concepts/type-conversion

concepts/numbers/introduction.md

@@ -9,3 +9,14 @@ Many programming languages have specific numeric types to represent different ty
 
 If you require arbitrary precision or work with extremely large numbers, use the `bigint` type.
 Otherwise, the `number` type is likely the better option.
+
+## Rounding
+
+There is a built-in global object called `Math` that provides various [rounding functions][ref-math-object-rounding]. For example, you can round-down (`floor`) or round-up (`ceil`) decimal numbers to nearest whole numbers.
+
+```javascript
+Math.floor(234.34); // => 234
+Math.ceil(234.34); // => 235
+```
+
+[ref-math-object-rounding]: https://javascript.info/number#rounding

exercises/concept/freelancer-rates/.docs/hints.md

@@ -2,17 +2,15 @@
 
 ## 1. Calculate the day rate given an hourly rate
 
-- Use the [numeric operators][ref-numeric-operators] from Lucian's Luscious Lasagna.
+- Use the arithmetic operators as mentioned in the introduction of this exercise.
 
-[ref-numeric-operators]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators
+## 2. Calculate the number of workdays given a budget
 
-## 2. Calculate the month rate, given an hourly rate and a discount
+- First determine the day rate, then calculate the number of days, and finally round that number down.
 
-- `100% - discount` equals the percentage after the discount is applied.
-- There is a built-in global object called [`Math`][ref-math-object] with functions to, for example, round-down (`floor`) or round-up (`ceil`).
+## 3. Calculate the discounted rate for large projects
 
-[ref-math-object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math
-
-## 3. Calculate the number of workdays given a budget, rate and discount
-
-- First determine the dayRate, given the discount, then calculate the number of days, and finally round that number down.
+- Round down the result from division to get the number of full months.
+- `100% - discount` equals the percentage charged after the discount is applied.
+- Use `%`, the remainder operator, to calculate the number of days exceeding full months.
+- Add the discounted month rates and full day rates and round it up

exercises/concept/freelancer-rates/.docs/instructions.md

@@ -1,19 +1,13 @@
 # Instructions
 
-In this exercise you will be writing code to help a freelancer communicate with a project manager by providing a few utility functions to quickly calculate day- and month rates, optionally with a given discount.
-
-We first establish a few rules between the freelancer and the project manager:
-
-- The daily rate is 8 times the hourly rate;
-- A month has 22 billable days.
-
-If the freelancer bills the project manager per month or more, there is a discount applied. This can be handy if the project manager has a fixed budget.
-
-Discounts are modeled as fractional numbers (percentage) between `0.0` (`0%`, no discount) and `0.90` (`90%`, maximum discount).
+In this exercise you will be writing code to help a freelancer communicate with his clients about the prices of certain projects. You will write a few utility functions to quickly calculate the costs for the clients.
 
 ## 1. Calculate the day rate given an hourly rate
 
-Implement a function to calculate the day rate given an hourly rate:
+A client contacts the freelancer to enquire about his rates.
+The freelancer explains that he **_works 8 hours a day._**
+However, the freelancer knows only his hourly rates for the project.
+Help him estimate a day rate given an hourly rate.
 
 ```javascript
 dayRate(89);
@@ -22,24 +16,26 @@ dayRate(89);
 
 The day rate does not need to be rounded or changed to a "fixed" precision.
 
-## 2. Calculate the month rate, given an hourly rate and a discount
+## 2. Calculate the number of workdays given a fixed budget
 
-Implement a function to calculate the month rate, and apply a discount:
+Another day, a project manager offers the freelancer to work on a project with a fixed budget.
+Given the fixed budget and the freelancer's hourly rate, help him calculate the number of days he would work until the budget is exhausted.
+The result _must_ be **rounded down** to the nearest whole number.
 
 ```javascript
-monthRate(89, 0.42);
-// => 9086
+daysInBudget(20000, 89);
+// => 28
 ```
 
-The discount is always passed as a number, where `42%` becomes `0.42`. The result _must_ be rounded up to the nearest whole number.
-
-## 3. Calculate the number of workdays given a budget, rate and discount
+## 3. Calculate the discounted rate for large projects
 
-Implement a function that takes a budget, a rate per hour and a discount, and calculates how many full days of work that covers.
+Often, the freelancer's clients hire him for projects spanning over multiple months.
+In these cases, the freelancer decides to offer a discount for every full month, and the remaining days are billed at day rate.
+**_Every month has 22 billable days._**
+Help him estimate his cost for such projects, given an hourly rate, the number of days the project spans, and a monthly discount rate.
+The discount is always passed as a number, where `42%` becomes `0.42`. The result _must_ be **rounded up** to the nearest whole number.
 
 ```javascript
-daysInBudget(20000, 89, 0.2002);
-// => 35
+priceWithMonthlyDiscount(89, 230, 0.42);
+// => 97972
 ```
-
-The discount is always passed as a `number`. `20.02%` is passed as `0.2002`. The result is the number of days should be rounded down to full days of work.

exercises/concept/freelancer-rates/.docs/introduction.md

@@ -12,6 +12,15 @@ Many programming languages have specific numeric types to represent different ty
 If you require arbitrary precision or work with extremely large numbers, use the `bigint` type.
 Otherwise, the `number` type is likely the better option.
 
+### Rounding
+
+There is a built-in global object called `Math` that provides various [rounding functions][ref-math-object-rounding]. For example, you can round-down (`floor`) or round-up (`ceil`) decimal numbers to nearest whole numbers.
+
+```javascript
+Math.floor(234.34); // => 234
+Math.ceil(234.34); // => 235
+```
+
 ## Arithmetic Operators
 
 JavaScript provides 6 different operators to perform basic arithmetic operations on numbers.
@@ -72,3 +81,4 @@ y %= 3; // y is now 1
 ```
 
 [mdn-operator-precedence]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#table
+[ref-math-object-rounding]: https://javascript.info/number#rounding

exercises/concept/freelancer-rates/.meta/config.json

@@ -1,7 +1,7 @@
 {
   "blurb": "Learn about numbers whilst helping a freelancer communicate with a project manager about day- and month rates.",
-  "authors": ["SleeplessByte"],
-  "contributors": [],
+  "authors": ["SleeplessByte", "JaPatGitHub"],
+  "contributors": ["junedev"],
   "files": {
     "solution": ["freelancer-rates.js"],
     "test": ["freelancer-rates.spec.js"],

exercises/concept/freelancer-rates/.meta/design.md

@@ -6,6 +6,8 @@
 - Know their underlying type (double precision).
 - Know their basic limitations (not all numbers can be represented, e.g. `0.1 + 0.2`).
 - Know how to truncate floating point numbers to a certain decimal place (`Math.ceil`, `Math.floor`, `Math.round`)
+- Know how to use arithmetic operators (`+`, `-`, `*`, `/`, `%`, `**`)
+- Learn about shorthand assignment operators (`+=`, etc.)
 
 ## Out of scope
 
@@ -15,6 +17,7 @@
 ## Concepts
 
 - `numbers`
+- `arithmetic-operators`
 
 ## Prerequisites
 

exercises/concept/freelancer-rates/.meta/exemplar.js

@@ -29,39 +29,32 @@ export function dayRate(ratePerHour) {
   return ratePerHour * 8;
 }
 
-/**
- * Calculates the rate per month
- *
- * @param {number} ratePerHour
- * @param {number} discount for example 20% written as 0.2
- * @returns {number} the rounded up monthly rate
- */
-export function monthRate(ratePerHour, discount) {
-  const monthly = dayRate(ratePerHour) * 22;
-  const discounted = applyDiscount(monthly, discount);
-  return Math.ceil(discounted);
-}
-
 /**
  * Calculates the number of days in a budget, rounded down
  *
  * @param {number} budget the total budget
  * @param {number} ratePerHour the rate per hour
- * @param {number} discount to apply, example 20% written as 0.2
  * @returns {number} the number of days
  */
-export function daysInBudget(budget, ratePerHour, discount) {
-  const discounted = applyDiscount(dayRate(ratePerHour), discount);
-  return Math.floor(budget / discounted);
+export function daysInBudget(budget, ratePerHour) {
+  return Math.floor(budget / dayRate(ratePerHour));
 }
 
 /**
- * Applies a discount to the value
+ * Calculates the discounted rate for large projects, rounded up
  *
- * @param {number} value
- * @param {number} percentage for example 20% written as 0.2
- * @returns {number} the discounted value
+ * @param {number} ratePerHour
+ * @param {number} numDays: number of days the project spans
+ * @param {number} discount: for example 20% written as 0.2
+ * @returns {number} the discounted rate, rounded up
  */
-function applyDiscount(value, percentage) {
-  return (1 - percentage) * value;
+export function priceWithMonthlyDiscount(ratePerHour, numDays, discount) {
+  const numMonths = Math.floor(numDays / 22);
+  const monthlyRate = 22 * dayRate(ratePerHour);
+  const monthlyDiscountedRate = (1 - discount) * monthlyRate;
+
+  const numExtraDays = numDays % 22;
+  const priceExtraDays = numExtraDays * dayRate(ratePerHour);
+
+  return Math.ceil(numMonths * monthlyDiscountedRate + priceExtraDays);
 }

exercises/concept/freelancer-rates/freelancer-rates.js

@@ -29,36 +29,25 @@ export function dayRate(ratePerHour) {
   throw new Error('Implement the dayRate function');
 }
 
-/**
- * Calculates the rate per month
- *
- * @param {number} ratePerHour
- * @param {number} discount for example 20% written as 0.2
- * @returns {number} the rounded up monthly rate
- */
-export function monthRate(ratePerHour, discount) {
-  throw new Error('Implement the monthRate function');
-}
-
 /**
  * Calculates the number of days in a budget, rounded down
  *
- * @param {number} budget the total budget
- * @param {number} ratePerHour the rate per hour
- * @param {number} discount to apply, example 20% written as 0.2
+ * @param {number} budget: the total budget
+ * @param {number} ratePerHour: the rate per hour
  * @returns {number} the number of days
  */
-export function daysInBudget(budget, ratePerHour, discount) {
+export function daysInBudget(budget, ratePerHour) {
   throw new Error('Implement the daysInBudget function');
 }
 
 /**
- * Applies a discount to the value
+ * Calculates the discounted rate for large projects, rounded up
  *
- * @param {number} value
- * @param {number} percentage for example 20% written as 0.2
- * @returns {number} the discounted value
+ * @param {number} ratePerHour
+ * @param {number} numDays: number of days the project spans
+ * @param {number} discount: for example 20% written as 0.2
+ * @returns {number} the rounded up discounted rate
  */
-function applyDiscount(value, percentage) {
-  throw new Error('Implement the applyDiscount function');
+export function priceWithMonthlyDiscount(ratePerHour, numDays, discount) {
+  throw new Error('Implement the priceWithMonthlyDiscount function');
 }