Alon and his friend Marna own a chimney sweep service company. Working together, they can clean a 20-foot chimney in 1 Five-sevenths hours. If it takes Kalon 4 hours to clean a 20-foot chimney by himself, how long does it take Marna to clean the same size chimney by herself?

3 hours

Step-by-step explanation:

Given that:

Time taken by Kalon = 4 hours

Time taken by Marna =?

Time taken if the work together = 1 5/7 hours

Kalon's rate = 1/ time =. 1/4

Kalon + Marna = 1 ÷ 1 5/7 = 7/12

Hence,

Marna's rate = 7/12 - 1/4

Marna's Rate = (7 - 3) / 12 = 4/12 = 1/3

Marna's rate = 1/3

Hence, time it takes Marna = reciprocal of rate = 1÷ 1/3 = 1 * 3/1 = 3 hours

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step-by-step explanation: