An engineer undertakes a project to build a road 10 km long in 30 days and employs 30 men for the purpose. After 10 days, he finds only 2 km of the road has been completed. Find the (approximate) number of extra men he must employ to finish the work in time.  Choices:  A) 30  B) 40  C) 50  D) 60  E) 70

Rationale: "30 workers working already let x be the total men required to finish the task in next 20 days 2 km done hence remaining is 8 km also , work has to be completed in next 20 days ( 30 - 10 = 20 ) we know that , proportion of men to distance is direct proportion and , proportion of men to days is inverse proportion hence , x = ( 30 * 8 * 10 ) / ( 2 * 20 ) thus , x = 60 thus , more men needed to finish the task = 60 - 30 = 30 answer : a"
Answer: A