In what ratio tea at Rs 240/kg should be mixed with tea at Rs 280/kg so that on selling the mixture at Rs 324/kg there is a profit of 20%?

1:3 : seems correct

Cost price $= 324\times\frac{100}{(100+20)}=324\times\frac{5}{6}=Rs. 270$

Let the ratio in which tea at Rs. 240/kg and Rs. 280/kg is mixed be $x:y$

$=> 240x+280y=270(x+y)$

$=> 24x+28y=27x+27y$

$=> 27x-24x=28y-27y$

$=> 3x=y$

$=> \frac{x}{y}=\frac{1}{3}$

=> Ans - (C)