Solution to: Containers and Cranes

Let's see how much of the load each crane can unload per hour.

Cranes A and B together take 2 hours to unload the entire load. This means they can unload 1 : 2 = ½ of the load per hour. Therefore, A + B = ½.

Cranes B and C can unload the load together in 2 hours and 15 minutes, which is equal to 2¼ hours. This means they can unload 1 : 2¼ = ⁴⁄₉ of the load per hour. Therefore, B + C = ⁴⁄₉.

Cranes A and C unload the load together in 3 hours and 36 minutes, which is equal to 3 ³⁄₅ hours. This means they can unload 1 : 3 ³⁄₅ = ⁵⁄₁₈ of the load per hour. Therefore, A + C = ⁵⁄₁₈.

Solving these three equations yields A = ¹⁄₆, B = ⅓ and C = ¹⁄₉. This means crane A takes 6 hours individually, crane B takes 3 hours, and crane C takes 9 hours.

Conclusion: crane B is the fastest option, completing the work in 3 hours.

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