A Sonar of a ship sends sounds waves of speed 1500 m/s. These waves are reflected back by the ocean floor in 5 seconds. Find the depth (in m) of the ocean floor.
The weights of 4 boxes are 100, 90, 80 and 40 kilograms. Which of the following cannot be the total weight, in kilograms, of any combination of these boxes and in a combination a box can be used only once?