A work that could be completed in 10 days was completed in 8 days as 5 more men joined at the start of work. What was the total number of men before the 5 men joined?

20

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 values in the formula,

⇒ M x 10 = (M + 5) x 8

⇒ 5M = 20 + 4M

⇒ M = 20.