Hi All,

This question can be solved with algebra or by TESTing THE ANSWERS. Here's how you can TEST THE ANSWERS:

We're told that both the left and right lanes receive a constant number of cars per hour.

We're also told two pieces of information based on hypotheticals:

1) If 700 cars per hour were transferred from the left lane to the right lane, then the number of cars in the right lane would be DOUBLE the number in the left.

2) If 700 cars per hour were transferred from the right lane to the left lane, then the number of cars in the left lane would be FOUR TIMES the number in the left.

We're asked how many cars enter the left lane per hour.

Let's TEST Answer B….

If….

1500 cars enter the left lane per hour, then (per the 1st hypothetical) the number entering the right lane would be 900 per hour

1500 - 700 = 800

900 + 700 = 1600

Right lane is DOUBLE the left lane

However, these values (1500 and 900) do NOT match the information in the second hypothetical:

900 - 700 = 200

1500 + 700 = 2200

Left lane is 11 TIMES the right lane

Eliminate Answer B

We need more cars in the left lane (to increase the number of cars in the right lane), but the answers are sufficiently "spaced out", that we probably won't need that many more...

Next, let's TEST Answer C…

If….

1700 cars enter the left lane per hour, then (per the 1st hypothetical) the number entering the right lane would be 1300 per hour

1700 - 700 = 1000

1300 + 700 = 2000

Right lane is DOUBLE the left lane

These values (1700 and 1300) ALSO match the information in the second hypothetical:

1700 + 700 = 2400

1300 - 700 = 600

Left lane is 4 TIMES the right lane

Final Answer:

GMAT assassins aren't born, they're made,

Rich

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