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A and B can do a piece of work in 12 days; B and C can do it in 15 days while C and A can finish it in 20 days. In how many days will A, B and C finish it, working together? In how many days will each of them finish it working alone?

Respuesta :

onyebuchinnaji

Answer:

  • It takes A 30 days to finish the work alone
  • It takes B 20 days to finish the work alone
  • It takes C 60 days to finish the work alone

  • Working together, it takes them 10 days to finish the work

Step-by-step explanation:

Given;

[tex]\frac{1}{A} + \frac{1}{B} =\frac{1}{12} \\\\\frac{1}{B} + \frac{1}{C} = \frac{1}{15}\\\\\frac{1}{A} + \frac{1}{C} = \frac{1}{20}\\\\[/tex]

From given equations above;

[tex]\frac{1}{A} +\frac{1}{B} = \frac{1}{12}\\\\But, \frac{1}{B} =\frac{1}{15} -\frac{1}{C}\\\\ \frac{1}{A} +\frac{1}{15} -\frac{1}{C}= \frac{1}{12}\\\\Also, \frac{1}{C} = \frac{1}{20} -\frac{1}{A} \\\\ \frac{1}{A} +\frac{1}{15} -(\frac{1}{20} -\frac{1}{A})= \frac{1}{12}\\\\ \frac{1}{A} +\frac{1}{15} -\frac{1}{20} +\frac{1}{A}= \frac{1}{12}\\\\ \frac{1}{A} +\frac{1}{A} = \frac{1}{12} +\frac{1}{20}-\frac{1}{15}\\\\\frac{2}{A} = \frac{300+ 180-240}{3600} \\\\\frac{2}{A} =\frac{240}{3600}\\\\[/tex]

[tex]\frac{2}{A} = \frac{1}{15} \\\\A = 30 \ days[/tex]

solve for B;

[tex]\frac{1}{A} + \frac{1}{B} = \frac{1}{12}\\\\ \frac{1}{B} = \frac{1}{12} - \frac{1}{A} \\\\ \frac{1}{B} = \frac{1}{12} - \frac{1}{30}\\\\ \frac{1}{B} =\frac{5-2}{60} \\\\ \frac{1}{B} =\frac{3}{60}\\\\B = 20 \ days[/tex]

Solve for C;

[tex]\frac{1}{C} =\frac{1}{20} -\frac{1}{A}\\\\ \frac{1}{C} = \frac{1}{20} -\frac{1}{30}\\\\ \frac{1}{C} =\frac{3-2}{60} \\\\ \frac{1}{C} =\frac{1}{60}\\\\C = 60 \ days[/tex]

When they work together;

[tex]\frac{1}{A} +\frac{1}{B} +\frac{1}{C} =\frac{1}{y} \\\\\frac{1}{30} +\frac{1}{20} +\frac{1}{60} = \frac{1}{y}\\\\\frac{2+ 3+ 1}{60} =\frac{1}{y}\\\\\frac{6}{60} =\frac{1}{y}\\\\y = 10\ days[/tex]

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