40 persons take 6 days to complete a certain task, working 10 hours a day. How many hours a day will be sufficient for 30 persons to complete the same task in 10 days?

8

Formula to be used here,

\( { M}_{1 } \) x \( { D}_{1 } \) x \( { H}_{1 } \)  = \( { M}_{2 } \) x \( { D}_{2 } \) x \( { H}_{2 } \)

where, M = no. of Men, D = No. of Days, H = No. of hours,

⇒ Putting values in the formula,

⇒ 40 x 6 x 10 = 30 x 10 x \( { H}_{2 } \)

⇒ \( { H}_{2 } \) = 8 hours.