David has some marbles. He gave 2/5 of his marble to his neighbour and 1/6 of the remainder to his friend Ali. He had 25 marbles left. How many marbles did he have at first?

Answer: he had 50 marbles at first.

Step-by-step explanation:

Let x represent the number of marbles that he had at first.

He gave 2/5 of his marble to his neighbour. It means that the number of marbles that he gave to his neighbour is 2/5 * x = 2x/5

The number of marbles that he has remaining is

x - 2x/5 = 3x/5

He gave 1/6 of the remainder to his friend Ali. It means that the number of marbles that he gave to his friend is

1/6 * 3x/5 = x/10

The number of marbles that he has left is

3x/5 - x/10 = 5x/10

He had 25 marbles left. It means that

5x/10 = 25

5x = 25 * 10 = 250

x = 250/5 = 50