If decreasing 120 by x% gives the same result as increasing 40 by x%, then x% of 210 is what percent less than (x+20)% of 180?

16\(\frac{2}{3}\) %

120 (100-x)% = 40 (100+x)%

     3 (100-x) = 100+x

 300 - 3x = 100+x

 300 - 100 = x +3x

           200 = 4x

             50 = x

⇒ x% of 210  =  50% × 210  = 105

⇒ (x+20)% of 180 =(50+20)% × 180 = 70% of 180 = 126 

 Difference 126 - 105 = 21

Percent less = \(\frac{21}{126}\) × 100 = 16\(\frac{2}{3}\) %