Clearly X={100,200,300,400,500,600,700,800,900} And for the equation x3−3ax2+(298a+299)x−2=0 to have positive point of maxima. The equation f′(x)=0 should have both the roots positive and unequal, which gives a>299. ∴Y={a;a>299} ∴ Number of elements in X∩Y=7