Project-Euler
Ruby

# Project Euler Problem 1 in Ruby

# 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 1. **

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# Problem 1

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23. Find the sum of all the multiples of 3 or 5 below 1000.

```
class Problem1
def question
"If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9.
The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000."
end
def sum_multiples_3_and_5 n
return 0 if(n <= 1)
if(n % 3 == 0 || n % 5 == 0)
n + sum_multiples_3_and_5(n - 1)
else
sum_multiples_3_and_5(n - 1)
end
end
def solve
sum_multiples_3_and_5(999)
end
def correct?
solve === answer
end
private
def answer
233168
end
end
```

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