Digging companies

Company A would dig a pit for 12 days, company B for 15 days, company C for 20 days and the company D for 24 days. Work began together companies C and D, but after three days joined them other two companies. How long took to dig a pit?

Result

x =  6 d

Solution:

x(1/20+1/24) + (x-3)(1/12+1/15) =1

29x = 174

x = 6

Calculated by our simple equation calculator.

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