A man can row 9$1\over 3$ kmph in still water and finds that it takes him thrice as much time to row upstream as to row downstream the same distance in the river. What is the speed of the stream?
The traffic lights at three different road crossings change every 21 seconds, 63 seconds and 105 seconds respectively. If they all change simultaneously at 9 : 15 : 00 AM, at what time will they again change simultaneously?
In an examination a student scores 7 marks for every correct answer and loses 1 mark for every wrong answer. If he attempts all 150 questions and scores 400 marks, the number of questions he attempts incorrectly is
A and B can do a piece of work individually in 9 and 18 days respectively. Both started working but A stopped 3 days before finishing. In how many days will the work be completed?
The volumes and radii of a right circular cylinder and a sphere are equal. If H is the height of the cylinder and D is the diameter of the sphere, then what is the relation between H and D?