Ratios, Proportions, Rates, and Percentages

/**
 * Fintech Math Bootcamp · Lesson 003 of 120
 * Ratios, Proportions, Rates, and Percentages
 * Module 01: Mathematical Language and Quantitative Reasoning
 *
 * Scenario: Comparing approval rates across merchants
 * Rule:     rate = approved / attempted
 *
 * Try it:   A 2% fee on 100 is how much?
 *
 * Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/mathematical-language-and-quantitative-reasoning/ratios-proportions-rates-and-percentages/
 * Free course:    https://courses.thefintechbuilder.com
 * Synthetic teaching example, not financial advice or a production library.
 */

export function lesson003() {
  const approved = 700;
  const attempted = 1000;
  if (attempted <= 0) throw new Error("No denominator");
  const rate = approved / attempted;
  const result = {rate, percent: 100 * rate};
  return result;
}

export const checkedResult = {"rate":0.7,"percent":70};

// Run this file directly: npx tsx lessons/01-mathematical-language-and-quantitative-reasoning/003-ratios-proportions-rates-and-percentages.ts
if (process.argv[1] && import.meta.url.endsWith(process.argv[1].replace(/\\/g, "/").split("/").pop()!)) {
  console.log(JSON.stringify(lesson003(), null, 2));
}

"""
Fintech Math Bootcamp · Lesson 003 of 120
Ratios, Proportions, Rates, and Percentages
Module 01: Mathematical Language and Quantitative Reasoning

Scenario: Comparing approval rates across merchants
Rule:     rate = approved / attempted

Try it:   A 2% fee on 100 is how much?

Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/mathematical-language-and-quantitative-reasoning/ratios-proportions-rates-and-percentages/
Free course:    https://courses.thefintechbuilder.com
Synthetic teaching example, not financial advice or a production library.

Run it: python main.py
"""

import json


def lesson003() -> dict:
    approved = 700
    attempted = 1000
    if attempted <= 0:
        raise ValueError("No denominator")
    rate = approved / attempted
    result = {"rate": rate, "percent": 100 * rate}
    return result


if __name__ == "__main__":
    print(json.dumps(lesson003(), indent=2))

/**
 * Fintech Math Bootcamp · Lesson 003 of 120
 * Ratios, Proportions, Rates, and Percentages
 * Module 01: Mathematical Language and Quantitative Reasoning
 *
 * Scenario: Comparing approval rates across merchants
 * Rule:     rate = approved / attempted
 *
 * Try it:   A 2% fee on 100 is how much?
 *
 * Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/mathematical-language-and-quantitative-reasoning/ratios-proportions-rates-and-percentages/
 * Free course:    https://courses.thefintechbuilder.com
 * Synthetic teaching example, not financial advice or a production library.
 *
 * Run it: javac Main.java && java Main
 */

public class Main {
    static final class ApprovalRate {
        final double rate;
        final double percent;

        ApprovalRate(double rate, double percent) {
            this.rate = rate;
            this.percent = percent;
        }
    }

    static ApprovalRate lesson003() {
        double approved = 700;
        double attempted = 1000;
        if (attempted <= 0) throw new IllegalArgumentException("No denominator");
        double rate = approved / attempted;
        ApprovalRate result = new ApprovalRate(rate, 100 * rate);
        return result;
    }

    public static void main(String[] args) {
        ApprovalRate result = lesson003();
        System.out.println(object("rate", num(result.rate), "percent", num(result.percent)));
    }

    // Formats a double the way JSON.stringify does: whole numbers without ".0", null for NaN or infinity.
    static String num(double x) {
        if (Double.isNaN(x) || Double.isInfinite(x)) return "null";
        if (x == Math.rint(x) && Math.abs(x) < 1e15) return String.valueOf((long) x);
        return String.valueOf(x);
    }

    static String quote(String text) {
        return "\"" + text.replace("\\", "\\\\").replace("\"", "\\\"") + "\"";
    }

    // Indents an already formatted JSON value by one level.
    static String nested(String json) {
        return json.replace("\n", "\n  ");
    }

    static String object(String... keysAndValues) {
        if (keysAndValues.length == 0) return "{}";
        StringBuilder out = new StringBuilder("{");
        for (int i = 0; i < keysAndValues.length; i += 2) {
            out.append(i == 0 ? "\n  " : ",\n  ")
               .append(quote(keysAndValues[i])).append(": ").append(nested(keysAndValues[i + 1]));
        }
        return out.append("\n}").toString();
    }
}

// Fintech Math Bootcamp · Lesson 003 of 120
// Ratios, Proportions, Rates, and Percentages
// Module 01: Mathematical Language and Quantitative Reasoning
//
// Scenario: Comparing approval rates across merchants
// Rule:     rate = approved / attempted
//
// Try it:   A 2% fee on 100 is how much?
//
// Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/mathematical-language-and-quantitative-reasoning/ratios-proportions-rates-and-percentages/
// Free course:    https://courses.thefintechbuilder.com
// Synthetic teaching example, not financial advice or a production library.
//
// Run it: go run main.go

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
)

type ApprovalRate struct {
	Rate    float64 `json:"rate"`
	Percent float64 `json:"percent"`
}

func lesson003() (ApprovalRate, error) {
	approved := 700.0
	attempted := 1000.0
	if attempted <= 0 {
		return ApprovalRate{}, errors.New("No denominator")
	}
	rate := approved / attempted
	result := ApprovalRate{Rate: rate, Percent: 100 * rate}
	return result, nil
}

func main() {
	result, err := lesson003()
	if err != nil {
		fmt.Fprintln(os.Stderr, "Error:", err)
		os.Exit(1)
	}
	printJSON(result)
}

// printJSON prints a value as JSON indented with two spaces, like JSON.stringify(value, null, 2).
func printJSON(value any) {
	out, err := json.MarshalIndent(value, "", "  ")
	if err != nil {
		panic(err)
	}
	fmt.Println(string(out))
}

/**
 * Fintech Math Bootcamp · Lesson 003 of 120
 * Ratios, Proportions, Rates, and Percentages
 * Module 01: Mathematical Language and Quantitative Reasoning
 *
 * Scenario: Comparing approval rates across merchants
 * Rule:     rate = approved / attempted
 *
 * Try it:   A 2% fee on 100 is how much?
 *
 * Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/mathematical-language-and-quantitative-reasoning/ratios-proportions-rates-and-percentages/
 * Free course:    https://courses.thefintechbuilder.com
 * Synthetic teaching example, not financial advice or a production library.
 *
 * Run it: g++ -std=c++17 -o main main.cpp && ./main
 */

#include <charconv>
#include <cmath>
#include <iostream>
#include <stdexcept>
#include <string>
#include <utility>
#include <vector>

// Formats a double the way JSON.stringify does: shortest round-trip form, null for NaN or infinity.
std::string num(double x) {
    if (!std::isfinite(x)) return "null";
    char buffer[32];
    auto [end, error] = std::to_chars(buffer, buffer + sizeof buffer, x);
    (void)error;
    return std::string(buffer, end);
}

std::string quote(const std::string& text) {
    std::string out = "\"";
    for (char c : text) {
        if (c == '"' || c == '\\') out += '\\';
        out += c;
    }
    return out + "\"";
}

// Indents an already formatted JSON value by one level.
std::string nested(const std::string& json) {
    std::string out;
    for (char c : json) {
        out += c;
        if (c == '\n') out += "  ";
    }
    return out;
}

std::string object(const std::vector<std::pair<std::string, std::string>>& fields) {
    if (fields.empty()) return "{}";
    std::string out = "{";
    for (std::size_t i = 0; i < fields.size(); ++i) {
        out += i == 0 ? "\n  " : ",\n  ";
        out += quote(fields[i].first) + ": " + nested(fields[i].second);
    }
    return out + "\n}";
}

struct ApprovalRate {
    double rate;
    double percent;
};

ApprovalRate lesson003() {
    const double approved = 700;
    const double attempted = 1000;
    if (attempted <= 0) throw std::invalid_argument("No denominator");
    const double rate = approved / attempted;
    const ApprovalRate result{rate, 100 * rate};
    return result;
}

int main() {
    const ApprovalRate result = lesson003();
    std::cout << object({{"rate", num(result.rate)}, {"percent", num(result.percent)}}) << "\n";
}

//! Fintech Math Bootcamp · Lesson 003 of 120
//! Ratios, Proportions, Rates, and Percentages
//! Module 01: Mathematical Language and Quantitative Reasoning
//!
//! Scenario: Comparing approval rates across merchants
//! Rule:     rate = approved / attempted
//!
//! Try it:   A 2% fee on 100 is how much?
//!
//! Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/mathematical-language-and-quantitative-reasoning/ratios-proportions-rates-and-percentages/
//! Free course:    https://courses.thefintechbuilder.com
//! Synthetic teaching example, not financial advice or a production library.
//!
//! Run it: rustc main.rs && ./main

struct ApprovalRate {
    rate: f64,
    percent: f64,
}

fn lesson003() -> Result<ApprovalRate, String> {
    let approved = 700.0;
    let attempted = 1000.0;
    if attempted <= 0.0 {
        return Err("No denominator".to_string());
    }
    let rate = approved / attempted;
    let result = ApprovalRate { rate, percent: 100.0 * rate };
    Ok(result)
}

fn main() {
    match lesson003() {
        Ok(result) => println!(
            "{}",
            object(&[("rate", num(result.rate)), ("percent", num(result.percent))])
        ),
        Err(message) => {
            eprintln!("Error: {}", message);
            std::process::exit(1);
        }
    }
}

/// Formats a number the way JSON.stringify does: shortest round-trip form, null for NaN or infinity.
fn num(x: f64) -> String {
    if x.is_finite() {
        format!("{}", x)
    } else {
        "null".to_string()
    }
}

fn quote(text: &str) -> String {
    format!("\"{}\"", text.replace('\\', "\\\\").replace('"', "\\\""))
}

/// Indents an already formatted JSON value by one level.
fn nested(json: &str) -> String {
    json.replace('\n', "\n  ")
}

fn object(fields: &[(&str, String)]) -> String {
    if fields.is_empty() {
        return "{}".to_string();
    }
    let lines: Vec<String> = fields
        .iter()
        .map(|(key, value)| format!("  {}: {}", quote(key), nested(value)))
        .collect();
    format!("{{\n{}\n}}", lines.join(",\n"))
}

/**
 * Fintech Math Bootcamp · Lesson 003 of 120
 * Ratios, Proportions, Rates, and Percentages
 * Module 01: Mathematical Language and Quantitative Reasoning
 *
 * Scenario: Comparing approval rates across merchants
 * Rule:     rate = approved / attempted
 *
 * Try it:   A 2% fee on 100 is how much?
 *
 * Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/mathematical-language-and-quantitative-reasoning/ratios-proportions-rates-and-percentages/
 * Free course:    https://courses.thefintechbuilder.com
 * Synthetic teaching example, not financial advice or a production library.
 *
 * Run it: dotnet run  (inside a console project that holds this Program.cs)
 */

using System.Text.Json;

var jsonOptions = new JsonSerializerOptions { WriteIndented = true, PropertyNamingPolicy = JsonNamingPolicy.CamelCase };
Console.WriteLine(JsonSerializer.Serialize(Lesson003(), jsonOptions));

static ApprovalRate Lesson003()
{
    const double approved = 700;
    const double attempted = 1000;
    if (attempted <= 0) throw new InvalidOperationException("No denominator");
    var rate = approved / attempted;
    var result = new ApprovalRate(rate, 100 * rate);
    return result;
}

record ApprovalRate(double Rate, double Percent);