Quandaries
and Queries 

Hi. My name is Sohaib. I am a student who has just been promoted to class 9. I came across this problem that I couldn't solve. This question was in the "quadratic equations" chapter. I need your help regarding this problem. Here it is. " A boat travels 12 km upstream and back in 1 hour 45 minutes. If the speed of the current is 3km/hr throughout, find the speed of the boat in still water, giving your answer correct to 3 decimal places." I would like to see the working too. Sohaib. 

Hi Sohaib, Suppose that the speed of the boat in still water is s km/hr, then against the current the boat travels at (s3) km/hr. The boat travels 12 km at this speed. How long does it take? With the current the boat travels at (s+3) km/hr. The boat travels 12 km at this speed. How long does it take? The sum of these two times is 1 ^{3}/_{4} hours. If you add the two times you found above and equate the sum to 1 ^{3}/_{4} you will have a quadratic equation that you can solve for s. Cheers, 

