8 persons can build a wall 140m long in 42 days. In how many days can 30 persons complete a similar wall 100 m long?  Choose the correct choice from the following choices:  A) 12  B) 10  C) 8  D) 6  E) 5

Rationale: explanation : more persons , less days ( indirect proportion ) more length of the wall , more days ( direct proportion ) ⇒ 8 × 100 × 42 = 30 × 140 × x ⇒ x = ( 8 × 100 × 42 ) / ( 30 × 140 ) = ( 8 × 100 × 14 ) / ( 10 × 140 ) = ( 8 × 100 ) / ( 10 × 10 ) = 8 . answer : option c
Answer: C