Tank A and Tank B are empty. Water flows from Tap X into Tank A at a rate of 6 liters per minute. Water flows from Tap Y into Tank B at a rate of 4 liters per minute. At the same time, water is drained from Tank A to Tank B at 3 liters per minute. If both taps start at the same time, how long will it take for Tank A to have twice as much water as Tank B?

Several questions from the 2017 paper gained notoriety for their deceptive simplicity or requirement for "lateral thinking" .

The total mass of a bag of flour and a bag of sugar was 10 kg. The mass of the flour was 1.8 kg more than the mass of the sugar. Mrs. Lim used $\frac14$ of the flour and $\frac13$ of the sugar to bake a cake. How much flour did she use?