CAT Exam 2021 Slot 3 Solved Paper

Let the alloy contain $x \Kg$ silver and $y \kg$ copper
Now when mixed with $3\Kg$ Pure silver
we get : ${x+3} / {x + y+ 3} = 9/10$
we get $10x + 30 = 9x + 9y + 27$
$9y - x = 3$
Now as per condition 2
silver in $2^{nd}$ alloy $= 2(0.9) =1.8 $
So we get -
${x+1.8} / {x + y+ 2} = 21/25$
we get $21y -4x =3$
solving (1) and (2) we get $y= 0.6$ and $x =2.4$
so $x + y = 3$