Pam gets on an elevator at the 12th floor of a building going up to

I may be wrong but A seems sufficient. They will probably meet at 46th floor, irrespective of time taken

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I guess A is sufficient here as Pam's elevator when it moves 2 floors up, simultaneously Hillary's elevator qill move 1 floor down.
Hence sufficient

Waiting for the OA

Thanks

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IMO A alone is sufficient to answer

Pam is at 12th floor and Hilary is at 63rd floor. Two people's elevators is moving in 2 opposite directions.

The distance between Pam and Hilary is 63 - 12 = 51 floors.

Let's call Pam's elevator speed is \(x\) floors per time unit.
Hilary's elevator speed is \(y\) floors per time unit.

Since they started moving, they would be at the same floor in: \(\frac{51}{x+y}\) time units.

Their paths would cross at floor: \(12+\frac{51x}{x+y}\).

(1) We have \(x=2y\). The question didn't say that \(x,y>0\).
Hence, if \(x=y=0\), they will never cross each other.
If \(x \neq 0\) and \(y \neq 0\), they will cross each other at floor: \(12+\frac{51 \times 2}{3}=46\).

Insufficient.

(2) Just know that \(y=4 \text{floors/second}\). There is no information about \(x\). Insufficient.

Combine (1) and (2): We have \(x=2y > 0\). Hence they will cross each other at 29th floor. Sufficient.

The answer is C.

A for me.

Since relative speeds are given, the point at which they will meet is the same irrespective of the actual value of speeds.

Solving crudely,
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62
63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46