In what proportion must a grocer mix tea priced respectively at Rs. 320 per kg and Rs. 560 per kg to make a mixture worth Rs. 480 per kg ?

The correct answer is (d) 0.50.

Let $x$ be the proportion of the cheaper tea and $1-x$ be the proportion of the more expensive tea. The total cost of the mixture is then $320x + 560(1-x) = 480$. Solving for $x$, we get $x = \frac{1}{2} = 0.50$.

In other words, the grocer must mix 1 part of the cheaper tea with 1 part of the more expensive tea to make a mixture worth Rs. 480 per kg.

Option (a) is incorrect because it would result in a mixture worth less than Rs. 480 per kg. Option (b) is incorrect because it would result in a mixture worth more than Rs. 480 per kg. Option (c) is incorrect because it is not a valid proportion.