# from https://www.tutorialspoint.com/program-to-implement-the-fractional-knapsack-problem-in-python
class FractionalKnapsack:
    def solve(self, weights, values, capacity):
        res = 0
        for pair in sorted(zip(weights, values), key=lambda x: - x[1]/x[0]):
            if not bool(capacity):
                break
            if pair[0] > capacity:
                res += int(pair[1] / (pair[0] / capacity))
                capacity = 0
            elif pair[0] <= capacity:
                res += pair[1]
                capacity -= pair[0]
        return int(res)

ob = FractionalKnapsack()
weights = [20, 50, 30]
values = [60, 100, 120]
capacity = 50
print(ob.solve(weights, values, capacity))

180