Question 1019965
Let x and y be the two original numbers.  
let x be increased by 40%.
Let r be the percentage by which y should be decreased.

Then we want 

xy = (1.4x)*(1-r)y
<==> 1 = 1.4(1-r)
==> 1 = 1.4 - 1.4r
==> 1.4r = 0.4
==> r = 2/7, or {{{28&4/7}}}%