they told you what you need to know - A, B, C, D are on a line, but not in this order.

Stat. (1) suggests this configuration: C is the midpoint between A and B, with a distance of 18/2=9 either way.

A----C----B

We know that C to D is 8, but we don't know in which direction: D could be to the left (AD---C----B) or right (A----C---DB) of C, and the distance from B to D (requested by the question stem) will be different in each of these scenarios. Stat. (2) mandates that A be to the left of D, but since CD is only 8 while AC is 18/2=9, this means that A is to the left of D in both the above configurations - so stat. (2) does not eliminate one of the scenarios, and there are still two possible values for the distance BD. Thus, combination is insufficient, and the answer is E.

Geva@MasterGMAT wrote:they told you what you need to know - A, B, C, D are on a line, but not in this order.

Stat. (1) suggests this configuration: C is the midpoint between A and B, with a distance of 18/2=9 either way.

A----C----B

We know that C to D is 8, but we don't know in which direction: D could be to the left (AD---C----B) or right (A----C---DB) of C, and the distance from B to D (requested by the question stem) will be different in each of these scenarios. Stat. (2) mandates that A be to the left of D, but since CD is only 8 while AC is 18/2=9, this means that A is to the left of D in both the above configurations - so stat. (2) does not eliminate one of the scenarios, and there are still two possible values for the distance BD. Thus, combination is insufficient, and the answer is E.

Thanks for the explanation Geva , I eliminated A and got confused when I came down to B. Got it now.

Deepthi Subbu wrote:
Thanks for the explanation Geva , I eliminated A and got confused when I came down to B. Got it now.

Drawing helps!