You have a set of cards numbered from one to nine, and these cards are to be divided into two groups.
If you want two groups with the cards in one group totalling twice the value of the other group, you could have 1, 5 and 9 in one group and 2, 3, 4, 6, 7 and 8 in the other group. The first group sums to 15 and the second group to 30, and 30 is twice 15.
However, your challenge is to put the cards into two groups with the cards in one group totalling three times the value of the other group.
The total value of the nine cards is 45, and when producing two groups with the value of one group twice the other you need to divide by three to get the total value of the smaller group. In this case 15 with the second group totalling 30.
The problem with one group totalling three times the other is that you have to divide by four, and four is not a factor of 45.
The clue is in the word twist, and the graphic of the number six accompanying this puzzle. You have to turn over the card with six on it to make nine. In this way the cards now total 48, which is divisible by four.
Dividing by four gives twelve, so the first group could be 1, 2 and 9, with the second group 3, 4, 5, 7, 8 and 9. There are other ways to split the cards.