20 workers can paint 24 walls in 36 days. In how many days can 30 workers paint 20 walls?

20

Formula to be used here, 

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

where, M = No. of men, D = No. of Days, W = Unit of Work,

⇒ Putting in the values,

⇒ \(\frac{20\;×\;36}{30\;×\;D_2}\) = \(\frac{24}{20}\)

⇒ \( { D}_{2 } \) = 20 days.