Given that 1 acre and 4,840 square yards are equal areas

Tricky one as everyone will divide 4840 by 220 and get 22 due to time crunch. But if you read the stem carefully, it is square yard, so, 4840/220*220 and you will get the answer. GMAT is all about catching these small tricks.

We need to determine the area in square furlongs.

To quickly solve such a unit conversion problem, we can simply multiply the corresponding unit conversion factors and the value to convert until all unnecessary units cancel out:

(1 fur²/40² rod²)(1 rod²/5.5² yd²)(4840 yd²/1 ac)(1 ac) =

4840/[(40²)(5.5²)] fur²

Since the answer choices are of different magnitudes, we can approximate the correct answer:

≈ 5000/(40 × 40 × 5 × 5) = 2/16 = 1/8 = 0.125 ≈ 0.1 fur²

Answer: B

For units conversion, simply keep plugging in the units. Check the discussion here first: https://anaprep.com/arithmetic-unit-conversion/

We will do the same thing here:


\(1 \text{ }acre = 4840 \text{ } yard^2 = 4840\text{ } yard * yard\)

1 rod = 5.5 yards which means 1 yard = 1/5.5 rods. So put this value in place of each yard.

\(1 \text{ }acre = 4840 * \frac{1}{5.5} * \frac{1}{5.5} \text{ }rod * rod\)

1 furlong = 40 rods which means 1 rod = 1/40 furlong. So put this value in place of each rod.

\(1 \text{ }acre = 4840 * \frac{1}{5.5} * \frac{1}{5.5} * \frac{1}{40} * \frac{1}{40} \text{ }furlong*furlong\)

Now for this calculation, simply approximate. 40 cancels 4840 so we have 121 which is about 3 times 40. Also, 5.5*5.5 is 30.25. So we get 3/30 approx which is 0.1

Answer (B)

Here is a video on how to estimate: https://youtu.be/4Wy7BrQrjkM
Here is a video on orally squaring numbers ending in 5: https://youtube.com/shorts/mZh5VayNNck