Three cups of water weigh 12 ounces. How heavy is 10 cups of water? \begin{tabular}{|c|c|} \hline \begin{tabular}{c} Cups of \\ water \end{tabular} & Weight \\ \hline 3 & 12 \\ \hline & \\ \hline & \\ \hline 10 & \\ \hline \end{tabular}

Step 1 ：Given that three cups of water weigh 12 ounces, we are asked to find the weight of 10 cups of water.

Step 2 ：This is a simple ratio problem. We can set up a proportion to solve for the unknown weight.

Step 3 ：The proportion would be \(\frac{3 \text{ cups}}{12 \text{ ounces}} = \frac{10 \text{ cups}}{x \text{ ounces}}\).

Step 4 ：Solving for x will give us the weight of 10 cups of water.

Step 5 ：By cross multiplying, we get \(3x = 120\).

Step 6 ：Solving for x, we get \(x = \frac{120}{3} = 40\).

Step 7 ：Final Answer: The weight of 10 cups of water is \(\boxed{40}\) ounces.