Question

A contractor who had a work force of 560 persons Have complete a portion of a stadium in 9 months . He was asked to complete in 7 months. How many extra persons he had to employ ?

Answer 1

560 persons   -----------9 months
 ?                    -----------7 months

they are in inverse proportion
so
560 x 9 / 7 =720
therefore 
no. of persons required to complete work in 7 months  = 720 persons

Answer 2

560 x 9 / 7 =720
therefore 
no. of persons required to complete work in 7 months  = 720 persons