Converting 2640 foot to mile can be simplified with mental math. Recognize that 2640 is exactly half of 5280, which is the number of feet in one mile. Therefore, 2640 foot is precisely 0.5 mile. This direct relationship makes it an ideal benchmark for quick estimations. For other values, remember the conversion factor 0.000189. Common mistakes include misplacing the decimal point or incorrectly applying the conversion factor (multiplying instead of dividing, or vice versa). Always double-check your calculation, especially for critical applications. A frequent error is confusing the US survey foot with the international foot, though the difference is negligible for most practical purposes at this scale. Another mistake is rounding too early in multi-step calculations, which can lead to significant cumulative errors. For professional precision, always use the exact conversion factor (1 mile = 5280 feet) and carry sufficient decimal places until the final result. Understanding the scale (downscale from foot to mile) helps confirm the logical direction of your answer.