20.
If 18 persons can build a wall 140 m long in 42 days, the number of days that
30 persons will take to complete a similar wall 100 m long, is. [CE I Tax 1993]
A.18 B.24
C.21 D.28
Answer: 18
Explanation: (Length 140:100) : (Persons 30:18) :: 42 : x
140
* 30 * x = 100 * 18 * 42 or x = 18
