A and B can finish a project in 10 days, B and C can finish it in 20 days, and C and A can finish it in 30 days. If A, B and C work together, they will finish the project in:
1
\(\frac{120}{11}\,\text{days}\)
2
\(\frac{110}{7}\,\text{days}\)
3
\(\frac{120}{7}\,\text{days}\)
4
\(\frac{130}{11}\,\text{days}\)