12 men or 20 boys can finish a work in 10 days. What part of the same work will be done by 4 men and 4 boys in 4 days?

$\frac{16}{75}$

Formula to be used here;

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

⇒ 12M x 10 = 20B x 10

⇒                M  :  B

Efficiency     5  :   3

⇒ Total Work = 12 (5) x 10 = 600 units.

⇒ Work done by 4 men and 4 boys in 4 days = \(\frac{W}{32}\) = 4 

⇒ W' = 128 units

⇒ W' is % of total work =  \(\frac{128}{600}\) = \(\frac{16}{75}\).