A farmer can plough a field working 6 hours per day in 25 days. The worker has to work how many hrs a day to complete the work in 15 days?

10 hrs

Assuming that the efficiency of the farmer and the worker is same,

\(\frac{M_1\;×\;D_1\;×\;H_1\;×\;E_1}{E_2\;×\;D_2\;×\;H_2\;×\;E_2}\) = \(\frac{W_1}{W_2}\)

⇒ \(\frac{6\; \times\; 25}{x\; \times\; 15}\) = 1 

(since no. of men is same and the work is same)

⇒                  x  = 10 hrs