42 boys can complete a piece of work in 20 days working 8 hours per day. In how many days can 14 boys complete the same work, each boy working 12 hours per day?

40 days

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 in the values,

⇒ 42 x 20 x 8 = 14 x \( { D}_{2 } \) x 12

⇒ \( { D}_{2 } \) = 40 days.