Answer:
She drank half of the hydroflask after lunch.
Explanation:
For simplicity let's say that the hydroflask held 100 fluid oz. If she drinks 1/4 of it before lunch then all we have to do is subtract 25 from 100 because 25 is 1/4 of 100. Then that leaves us with 75 fluid oz. Now after lunch she drinks 2/3 of what's left. So we divide 75 by 3 to find out what 1/3 of what's left is. 75/3 is 25. Now we just multiply 25 by 2 so we can get 2/3 of what's left. 25x2 is 50. Now the last step is to take what she drank after lunch (50 fluid oz.) and divide it by the total (100 fluid oz.) And 50/100 is 1/2. So she drank half after lunch.