Project-Euler
Ruby

# Sum of Even Fibonacci Numbers

# What is Project Euler

Project Euler is a website with a collection of programming and mathematical problems. Each challenge varies in difficulty and there are over 600 challenges. I highly recommend anyone interested in puzzles and programming to create an account and start solving. About Project Euler

** Stop here if you have not yet tried and solved Problem 2. **

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# Problem 2

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:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

```
class Problem2
require 'benchmark'
def question
"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:
1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms."
end
def fibonacci_even_sum(limit = 4000000)
sum = 2
runner = 2
one_back = 1
two_back = 0
while(runner <= limit)
sum += runner if runner.even?
two_back = one_back
one_back = runner
runner = two_back + one_back
end
sum
end
def solve
fibonacci_even_sum
end
def benchmark
Benchmark.measure { solve }
end
def correct?
solve === answer
end
private
def answer
4613732
end
end
```

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