Final answer:
The new weight of the water contained in the jar after some has been poured out is 4 ounces. This is calculated based on the initial total weight and percentage of water, and the percentage of water after pouring some out.
Step-by-step explanation:
You're asking about how to find the new weight of the water in a jar after some of it has been poured out, given that the water and sand weighs 10 ounces initially, and the water initially comprises 90% of total weight. After pouring out some water, the water now makes up 80% of the weight.
Initially, if the jar with water and sand weighs 10 ounces and the water is 90% of that weight, then the weight of the water is 0.9 * 10 = 9 ounces. The weight of the sand, which is not changing, is 10 - 9 = 1 ounce.
After some water is poured out, the total weight of the jar is the weight of the unchanged sand (1 ounce) plus the new weight of the water. Let's say the new weight of the jar is W ounces. According to the problem, the water is now 80% of the new total weight. So, the equation is 0.8 * W = weight of the water. Since the weight of the sand is 1 ounce and it does not change, W = weight of the water + 1 ounce. Substituting the first expression into this equation we get 0.8 * W + 1 = W. Solving for W gives us W = 5 ounces. Therefore, the weight of the water now is 0.8 * 5 = 4 ounces.