30 men can complete a piece of work in 24 days. 12 days after they started working together, 10 more men joined them. How many days will they now take to complete the remaining work?

9 days

Formula to be used here, 

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

where, M = No. of Men, D = No. of Days,

⇒ Putting in the formula,

⇒ 30 x 12 = 40 x \( { D}_{2 } \)

⇒ \( { D}_{2 } \) = 9 days,