let the circle between B and C be X ,so C is 2X,as it is the parent circle of the first one ,then the circle down from C is 4X ,left from which is 8X ,the nD is 16X . On the other hand,B is 2X,left from B is 4X ,then A is 8X .
So D is double of A .

Hi Rajibuddin,

This IR prompt is similar to a Quant PS Sequence question; you'll probably find it easiest to TEST VALUES to get to the correct answer.

Based on the description, we're told that when a node (a circle) has an arrow pointing to another node (another circle), there's a relationship between the two values. The first circle (the parent node) has a value that is DOUBLE that of the second circle (the child node; the one that is pointed TO).

As an example, look at the first 2 circles (the "A" and the one that "A" is pointing to). Those circles COULD have respective values of 2 and 1, 4 and 2, 6 and 3, 8 and 4, etc. To be fair, the prompt did NOT state that the values had to be integers, so we could have 3 and 1.5, 2.08 and 1.04, etc.

By extension, a longer "string" of nodes must also have values that DOUBLE from node to node. Notice the 3 circles (the "A", the "blank" and the "B"). Their respective values could be 4-2-1, 8-4-2, 12-6-3, 10-5-2.5, etc.

These examples are note-worthy in that they show how TESTing VALUES can help you to figure out the relationships of the various nodes. This question asks us to find 2 nodes - one that has DOUBLE the value of another.

Let's start with the 4th node (the one between the "B" and "C" nodes). Let's give THAT node a value of 1. DOUBLING each value as we go, we'd have....

1....2 (the "B" node)....4......8 (the "A" node)

Now, going in the other direction...
1....2 (the "C" node)....4....8.....16 (the "D" node)

From this, we can see that the "D" node is DOUBLE the "A" node.

Thus, the correct answer is .

GMAT assassins aren't born, they're made,
Rich
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Child Node (arrow head) = (1/2) of Parent node.
Assign place values as under and solve.