Plzz ignore my previous reply.. dont know how to delete that... :? See Square root of a no can be +ve or -ve And Sqaure root of a -ve no is not possible, its undefined So for this question if x<0 , then Sq.Root(-x*|x|) is assume x=-4 Sq.Root(-(-4)*|-4|) = Sq.Root (4*4) = Sq.Root (16 ) = +4 or -4 So ...

Hey!!! this is the way u do it : he wants to dowble his commission from $400 to $800 100+200+250+700+1000+x+y ---------------------------------------- = 800 7 i.e 2250+x+y = 5600 x+y = 3350 Now he has to sell 10/100 * z = 3350 z= 33500 He has to sell 33500 in order to double his average