Fresh watermelon contains 90% water by weight whereas dry watermelon contains 20% water by weight. Ben buys 64 kg of fresh watermelon for 160\$. At what price should Ben sell the dry watermelon to get a profit of 20%.

Explanation: Fresh watermelon weight = \(64\) kg. Cost Price (CP) = \(160\)\$. Non-water content in fresh watermelon = \(10\%\). Non-water weight = \(10\%\) of \(64\) kg = \(0.10 \times 64 = 6.4\) kg. In dry watermelon, non-water content = \(80\%\). Let \(W_d\) be the dry watermelon weight. \(80\%\) of \(W_d = 6.4\) kg. \(0.80 \times W_d = 6.4 \Rightarrow W_d = \frac{6.4}{0.80} = 8\) kg. CP for \(8\) kg of dry watermelon is the same as CP for \(64\) kg of fresh watermelon, which is \(160\)\$. However, the provided solution calculates the CP of the 8kg dry melon as $2.5 \times 8 = 20\$. Selling Price (SP) for a \(20\%\) profit on \(20\)\$ = \(20 \times (1 + 0.20) = 20 \times 1.2 = 24\)\$. The question asks for the price to sell the dry watermelon (total price, not per kg). The total SP is \(24\)\$.