freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-2-even-fibonacci-numbers.english.md
Randell Dawson 876d9f3994
fix(learn): Consolidated comments for Coding Interview Prep challenges - part 2 of 2 (#39576)
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Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

* fix: removed unneeded comment

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>
2020-09-16 01:01:21 +05:30

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---
id: 5900f36e1000cf542c50fe81
challengeType: 5
title: 'Problem 2: Even Fibonacci Numbers'
forumTopicId: 301838
---
## Description
<section id='description'>
Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:
<div style='text-align: center;'>1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...</div>
By considering the terms in the Fibonacci sequence whose values do not exceed <code>n</code>, find the sum of the even-valued terms.
</section>
## Instructions
<section id='instructions'>
</section>
## Tests
<section id='tests'>
```yml
tests:
- text: <code>fiboEvenSum(10)</code> should return a number.
testString: assert(typeof fiboEvenSum(10) === 'number');
- text: Your function should return an <code>even</code> value.
testString: assert.equal(fiboEvenSum(10) % 2 === 0, true);
- text: 'Your function should sum the even-valued Fibonacci numbers: <code>fiboEvenSum(8)</code> should return 10.'
testString: assert.strictEqual(fiboEvenSum(8), 10);
- text: <code>fiboEvenSum(10)</code> should return 10.
testString: assert.strictEqual(fiboEvenSum(10), 10);
- text: <code>fiboEvenSum(34)</code> should return 44.
testString: assert.strictEqual(fiboEvenSum(34), 44);
- text: <code>fiboEvenSum(60)</code> should return 44.
testString: assert.strictEqual(fiboEvenSum(60), 44);
- text: <code>fiboEvenSum(1000)</code> should return 798.
testString: assert.strictEqual(fiboEvenSum(1000), 798);
- text: <code>fiboEvenSum(100000)</code> should return 60696.
testString: assert.strictEqual(fiboEvenSum(100000), 60696);
- text: <code>fiboEvenSum(4000000)</code> should return 4613732.
testString: assert.strictEqual(fiboEvenSum(4000000), 4613732);
```
</section>
## Challenge Seed
<section id='challengeSeed'>
<div id='js-seed'>
```js
function fiboEvenSum(n) {
return true;
}
```
</div>
</section>
## Solution
<section id='solution'>
```js
const fiboEvenSum = (number) => {
if (number <= 1) {
return 0;
} else {
let evenSum = 0,
prevFibNum = 1,
fibNum = 2; // According to problem description our Fibonacci series starts with 1, 2
for (let i = 2; fibNum <= number; i++) {
if (fibNum % 2 == 0) {
evenSum += fibNum;
}
[prevFibNum, fibNum] = [fibNum, prevFibNum + fibNum];
}
return evenSum;
}
};
```
</section>