Remaining empty: ( 1 - \frac{7}{12} = \frac{5}{12} ) tank.
In 2 hours: ( 2 \times \frac{7}{24} = \frac{14}{24} = \frac{7}{12} ) tank filled. 2017 psle math questions and answers
Time needed = ( \frac{\text{remaining}}{\text{rate}} = \frac{\frac{5}{12}}{\frac{5}{12}} = 1 ) hour. Remaining empty: ( 1 - \frac{7}{12} = \frac{5}{12} ) tank
After turning off C, rate of A + B = ( \frac{1}{6} + \frac{1}{4} = \frac{4}{24} + \frac{6}{24} = \frac{10}{24} = \frac{5}{12} ) tank/hour. 2017 psle math questions and answers