How much weight can you lift by applying 100 lbs. of force to a twofold purchase rigged to disadvantage (do not consider friction)?

Correct Answer: Option C — 400 lbs.

A twofold purchase consists of two double blocks. Rigged to disadvantage, the mechanical advantage equals the number of parts of the fall at the moving block, which is four. Therefore, 100 lbs of force multiplied by a mechanical advantage of four results in a total lift of 400 lbs.