Siti had half as much as Fatimah: Siti = \(\frac{1}{2}\) Fatimah.
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• Let Fatimah = F ml. Then Siti = \(\frac{F}{2}\) ml
• After drinking: Siti = \(\frac{F}{2}\) − 50, Fatimah = F − 150
• Ratio after: (\(\frac{F}{2}\) − 50) : (F − 150) = 3 : 5
• 5(\(\frac{F}{2}\) − 50) = 3(F − 150)
• \(\frac{5F}{2}\) − 250 = 3F − 450
• \(\frac{5F}{2}\) − 3F = −200
• \(\frac{−F}{2}\) = −200 → F = 400
Fatimah had 400 ml of water at first.
Check: Siti = 200 ml. After: Siti 150 ml, Fatimah 250 ml. 150 : 250 = 3 : 5. ✓