Question 852499
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Hi,
Let x represent the constant of proportionality
If 10 is added to the middle number, the number form a G P.
&#8658; {{{(5x+10)/2x = 8x/(5x+10)}}}
 9x^2 + 100x + 100 = 0
(9x + 10)(x + 10) = 0,   x = -10
Numbers are; -20, -50, - 80  
and 
{ -20, (-50+ 10), - 80 } is {-20, -40, -80} a G.P