30 men working 8 hours per day can dig a pond in 16 days. By working how many hours per day can 32 men dig two same ponds, in 20 days?

12 hours per day

Formula to be used here, 

⇒ \(\frac{M_1\;×\;D_1\;×\;H_1}{M_2\;×\;D_2\;×\;H_2}\) = \(\frac{W_1}{W_2}\)

where, M = No. of Men, D = No. of Days, H = No. of Hours, W = Work,

⇒ Putting values in the formula,

⇒ \(\frac{30\;×\;16\;×\;8}{32\;×\;20\;×\;H_2}\) = \(\frac{1}{2}\),

⇒ \( { H}_{2 } \) = 12 hrs.